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Floating treatment wetlands (FTW) are an emerging Nature Based Solution that have exhibited promising nitrogen removal under different range of effluents pollutant concentrations. Despite the notable increase in the number of FTW studies in the last years, nitrogen (N) removal mechanisms within FTW have not been fully assessed. The present study aims to understand N removal in FTW and investigate their microbial biofilm activity through a pilot scale experiment for agri-food tertiary wastewater treatment. A conventional and a modified (with added cellular concrete (CC)) FTW were monitored over 7 months with respect to two control lagoons (conventional lagoons with or without CC hanging in the water column). Experimental results revealed that the best TN removal was achieved by the lagoon equipped with the modified FTW (20% mean removal increase compared to the conventional lagoon). Biofilm denitrification activity potential was up to 6.7–9.0 times higher within pilot lagoons equipped with FTW than that in control lagoon (LC without FTW), while nitrification activity potential was prominent in biofilms within the control pilot lagoons (exhibiting high dissolved oxygen (DO) concentration). Biofilms from plant roots exhibited the highest overall dissolved inorganic nitrogen treatment followed by the biofilms from sediments and CC material. Plant root biofilms exhibited both significant nitrification and denitrification activity potentials despite the overall low DO and COD concentrations within FTW pilot lagoons' water column. This suggests the existence of micro sites in the roots network which provide adequate aerobic conditions and access to organic carbon most probably through root exudates. Overall, N accumulation in the sediment was a minor removal mechanism for all pilot lagoons. Plant accumulation (accounting for one third of TN removal), nitrification and enhanced denitrification appeared to be the main removal mechanisms in pilot lagoons equipped with FTWs (with or without CC) while nitrification, algal assimilation and NH 4 -N volatilization may have been the major processes driving TN removal in the control pilot lagoons. Hence, FTW could be an interesting retrofit of existing lagoons to promote nitrogen removal through denitrification and plant assimilation, especially in the case of receiving bodies highly sensitive to nitrate input. Further research should address optimizing FTW design to guarantee stable N removal under changing water temperature and mitigate seasonal variations as well as investigate biofilm species for in-depth understanding of N cycle within FTWs. [ABSTRACT FROM AUTHOR]

The presence of non-reactive phosphorus (NRP) in environmental waters presents a potential risk of eutrophication and poses challenges for the removal of all phosphorus (P) fractions. This study presents the first investigation on the removal performance and mechanism of three model NRP compounds, sodium tripolyphosphate (STPP), adenosine 5′-monophosphate (AMP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), in the sediment microbial fuel cell-floating treatment wetland (SMFC-FTW). Coupling SMFC with plants proved to be effective at removing NRP via electrochemical oxidation and plant uptake, particularly the challenging-to-degrade phosphonates that contain C–P bonds. Compared with the control group, the removal efficiencies of the model NRP in SMFC were observed to increase by 11.9%–20.8%. SMFC promoted the conversion of NRP to soluble reactive phosphorus (sRP) and the transfer of P to sediment. Furthermore, the electrochemical process enhanced both plant growth and P uptake, and increased P assimilation by 72.6%. The presence of plants in the bioelectrochemical system influenced the occurrence and fate of P by efficiently assimilating sRP and supporting microbial transformation of NRP. Consequently, plants enhanced the removal efficiencies of all P fractions in the overlying water. This study demonstrated that SMFC-FTW is a promising technology to remove various NRP species in environmental waters. [Display omitted] • Coupling SMFC with plants can effectively degrade various NRP species. • SMFC facilitated the NRP conversion to RP in the overlying water and sediments. • Electrochemical treatment enhanced plant growth and P uptake. • Plants improved the removal efficiencies of all P fractions. [ABSTRACT FROM AUTHOR]

With the wide application of floating treatment wetland (FTW), the limited performance of FTWs should be improved. A comprehensive review is accordingly necessary to summarize the state-of-the-art on FTWs for performance improvement. An attempt has been made to gain information from literature about technologies to enhance the performance of FTWs. These technologies have been classified into three categories according to their mechanisms: 1) increasing the amount and activity of bacteria; 2) enhancing the growth of plant; and 3) configurable innovations. The design and application of each enhanced FTW have been discussed in detail. Thereafter, all the technologies have been compared and analyzed according to their improvement in pollutant removal and ecological effects. In summary, FTW with additional bio-carriers has a higher potential for future applications with the benefits of wide application conditions, scale-up potential, and the easy combination with other methods to further improve the removal efficiency. The stability and sustainability of these technologies should be further investigated. [Display omitted] • The state-of-the-art of intensified FTW was summarized. • Bio-carriers were found to be the most attractive intensified technology. • The appropriate technological combination should base on the wastewater conditions. • The resilience and sustainability of intensified FTW should be further evaluated. [ABSTRACT FROM AUTHOR]

Treatment wetlands are ecological systems that are engineered to improve polluted water quality through macrophyte, soil, and microbial remediation and are used commonly for urban and agricultural runoff treatment. However, constructed wetlands used for marine aquaculture effluent treatments are understudied when compared to their freshwater counterpart. We compared the nutrient retention and the microbial communities of two types of constructed wetland mesocosms, a vertical-flow treatment wetland (VFTW) and floating treatment wetland (FTW) in subtropical south Florida. To enhance nutrient retention efficiency, we implemented biodegradable plastic (polycaprolactone), as an external carbon source and monitored the performance of VFTW and FTW for the treatment of marine aquaculture effluent. Polycaprolactone surface were covered by various cyanobacterial genera including Oscillatoria , Leptolyngbya , Brasilonema , and Trichormus and some plastic-degrading bacteria such as Pseudomonas. The presence of a biodegradable plastic in FTW improved the overall performance of nitrogen removal (nitrite plus nitrate) by 14% through denitrification. The pattern of nutrient removal between two treatment wetland mesocosms were significantly different (p < 0.01), with over 87–91% retention of total nitrogen in VFTW and no retention in FTW, the latter due to poor retention of nitrite plus nitrate and production of organic nitrogen from the system not present in inflow waters. Total phosphorus was retained in both mesocosm types, with higher retention (74–81%) in the VFTW than in the FTW (17–40%). The nutrient retention in VFTW was higher overall compared with FTW mesocosms regardless of biodegradable plastic presence. [ABSTRACT FROM AUTHOR]

Eutrophic conditions occur when waterbodies accumulate excessive nutrients, which leads to algae growth, depleted dissolved oxygen, and increased turbidity. To improve water quality, a biological-chemical treatment was implemented using floating treatment wetlands (FTWs) and slow-release lanthanum delivered through airlift pumps. FTWs remove nutrients via plant uptake and denitrification while lanthanum binds and precipitates phosphate from the water column. The study sites, Densmore and Wilderness Ridge Ponds, had two FTWs and two lanthanum airlift pumps installed in 2020 and 2021. Our hypothesis was that if the biological-chemical treatment reduced nitrate and phosphate, algae growth would be limited, water clarity would improve, and benthic vegetation would increase. Chlorophyll- a , the photosynthetic pigment found in plants and algae, was analyzed to create a direct correlation to algae content within waterbodies. Chlorophyll- a samples were collected twice a month at strategically selected, georeferenced locations in both ponds between May and October in 2022. Water samples were collected when the European Union's Sentinel-2 multispectral satellite passed over the study sites. To estimate chlorophyll- a concentrations prior to the biological-chemical treatment, a correlation was developed between the collected chlorophyll- a concentrations and Sentinel-2 band algorithms. Sentinel-2 imagery provided a means to analyze how chlorophyll- a fluctuated before and during treatment. We found the novel band algorithm, 3BR1, had the best correlation (R2 = 0.72). Applying this band ratio for Sentinel-2 images from 2019 to 2022, a Tukey's HSD test analyzed monthly differences between years. The FTW and lanthanum treatment reduced chlorophyll- a concentrations in Densmore Pond, but not in Wilderness Ridge Pond. One likely reason was Wilderness Ridge Pond had a complex irrigation system and was continuously replenished with nitrate-rich groundwater. Our results show Sentinel-2 can be used to predict historical chlorophyll- a concentrations by using the novel 3BR1 band algorithm and that FTWs and lanthanum can effectively reduce algal growth. [ABSTRACT FROM AUTHOR]

The present study had as objective to evaluate the influence of different operation conditions on two treatment systems composed of anerobic biofilter (AF) and hybrid constructed wetlands (CWs). Both treatment lines had as the first treatment stages an 1450 L AF unit and a CW designed as a Floating Treatment Wetland. Then, a pump directed half of the wastewater flow for each of the treatment lines. One of the lines was composed of a Vertical Flow CW incorporated with microbial fuel cells (CW-MFC), called Configuration 1 (C1), whereas the other line consisted of a Vertical Flow CW (VFCW) and a Horizontal Flow CW (HFCW), named Configuration 2 (C2). The treatment system was fed with wastewater generated in a university campus and monitored for 13 months, with three operation conditions tested: 3 pulses per day with 50 L each (20.5 L/m2day); 4 pulses with 75 L each (41 L/m2day) and 6 pulses with 75 L each (61.6 L/m2day). In addition, the potential bioenergy generated was monitored. For the last operation condition, C1 efficiently reduced BOD 5 (88.7%) and turbidity (84.4%). On the other hand, for the nutrients the treatment efficiencies were lower, with 40.3% (TP) and 46.6% (N−NH 3). Overall, similar results were obtained with the C2, with mean removal efficiencies of BOD 5 (87.3%), turbidity (93.1%), and lower TP (10.4%) reduction. The treatment performance presented similar tendencies even with the changes in loading rates and in hydraulic retention times. Regarding the voltage monitoring, a peak of 687 mV was obtained considering a mean loading rate of 15.6 gCOD/m2day, whereas the maximum power density was 0.25 mW/m. Future research should focus on reducing the internal resistance of the CW system, thus increasing the bioelectricity generated and in treating wastewater with higher organic matter content. [Display omitted] [ABSTRACT FROM AUTHOR]

Floating treatment wetlands (FTWs) are an innovative type of phytoremediation technique being used to reduce the impact of excess nutrient loading. Plants hydroponically grown on FTWs take up nutrients from water through their roots. In general microbial communities in the rhizosphere are important for healthy growth and nutrient uptake by plants. Despite most of previous studies focused on the nutrient removal processes, very little is known about microbial communities associated with FTW plant roots. The purpose of this study was to characterize the microbiomes revolving around the submerged roots of FTW in a manmade stormwater pond and to elucidate the source of FTW plant root microbiomes. The microbial communities collected from the plant roots Canna flaccida (golden canna) and Juncus effusus (soft rush), biofilms of plant pot (polyethylene) and floating mat foam (closed-cell urethane), and surrounding water were studied using 16S rRNA gene amplicon sequencing. The FTW plant root microbiomes were dominated by Alphaproteobacteria and Cyanobacteria at the class level, and Anabaena , Rhizobium and Rhodobacter at the genus level. Microbial communities of the FTW plant roots showed unique compositions resembling most closely the surrounding water samples while being quite different from the biofilm samples, leading the conclusion that the major source of microbial populations was the surrounding water. However, the dominance of Rhizobium species was only observed in the two plant roots and not recognized in the surrounding water samples, indicating that the FTW roots may selectively shape root microbiomes. Unexpectedly, quite a few groups of microbes were associated with the sulfur cycle. This finding indicates that the oxic-anoxic gradient is formed in the FTW rhizosphere, and this environmental gradient assists to extend the phylogenetic and functional diversities of microorganisms. We anticipate the presence of intrinsic rhizosphere microbiomes and the importance of complex biogeochemical processes that include carbon, sulfur and nitrogen driven by physical activity and chemical releases of FTW plant roots. [ABSTRACT FROM AUTHOR]

This work evaluated depuration performance and macrophyte plants growth in a full-scale hybrid-constructed wetland (H-CW) (1000 population equivalent) treating municipal wastewater. The plant was activated in June 2010 after a restoration of an existent H-CW composed of a horizontal subsurface flow (HSSF) bed vegetated with evergreen xerophile species ( Prunus laurocerasus , Pittosporum spp., Elaeagnus angustifolia ), connected with a sedimentation pond vegetated with Lemna spp. To enhance the depuration performances, in both sections of the plant the original vegetation was removed and the HSSF bed was vegetated with Phragmites australis , whereas in the pond, a floating treatment wetland vegetated with Iris pseudacorus was installed. The depuration performance in treating total nitrogen (TN), nitrate nitrogen (NO 3 -N), ammonia nitrogen (NH 4 -N), total phosphorus (TP), orthophosphate (PO 4 -P) and chemical oxygen demand (COD) was weekly monitored between August 2010 and August 2011. Results indicated median concentration abatements for the entire system of 74.3% for TN, 62.1% for NH 4 -N, 77.7% for NO 3 -N, 29.6% for TP, 37.4% for PO 4 -P, and 46.7% for COD. In addition, at the end of the first growing season (June 2010–November 2010), good adaption to the system was detected for both P. australis and I. pseudacorus , which produced respectively 3.9 ± 2.2 kg m −2 and 3.7 ± 1.0 kg m −2 of above-ground dry biomass, with average above-ground N uptakes of 62.4 ± 35.6 g m −2 and 69.8 ± 19.0 g m −2 and average above-ground P uptakes of 4.6 ± 2.6 g m −2 and 7.8 ± 2.1 g m −2 . The results indicate that a H-CW composed of a sequence of HSSF bed and FTW represents an effective application for abating TN, NH 4 -N, NO 3 -N and COD concentrations from municipal wastewater. [ABSTRACT FROM AUTHOR]

Two different chemical recipes comprising various pollutants were selected to create high (HC) and low (LC) levels of contaminated synthetic greywaters (SGW). Remediation in macrocosm–scale floating treatment wetlands (FTW) vegetated with Phragmites australis (Cav.) Trin. ex Steud. (common reed) was investigated under natural weather conditions. The presence or absence of vegetation, short or long contact time of treatment, and low or high contamination loads are the main operational variables in the experimental set-up design of the FTW. The focus on removal processes (other than sedimentation) such as the role of macrophytes in phytoremediation was achieved by agitation of the treated outflow before sampling. To assess the impact of interactions between the experimental operational variables on removal performances of FTW, different approaches of statistical analysis were applied. The results revealed that total suspended solids (TSS) and turbidity values dropped significantly ( p < 0.05) in the presence of vegetation compared with those values from unvegetated wetlands. The presence of vegetation can significantly ( p < 0.05) improve the biodegradation possibility of greywater by increasing the five-day biochemical oxygen demand (BOD) and decreasing the chemical oxygen demand (COD) concentrations. In vegetated FTW, higher removal rates of COD can be achieved when treating HC-SGS compared to LC-SGW. However, no significant differences ( p > 0.05) in the removal of BOD was noted. Significant increases ( p < 0.05) in BOD concentrations have been recorded with increasing contact time of treatment, while high removals of COD have been recorded. The presence of vegetation in wetlands affected significantly ( p < 0.05) the decrease of dissolved oxygen (DO) concentrations in outflow of both types of greywater. If limited sources of organic matter are available, vegetation has significantly ( p < 0.05) enhanced the nutrient balance with increasing nitrate-nitrogen (NO 3 -N) and decreasing ortho-phosphate-phosphorus (PO 4 -P) concentrations in the outflow. Furthermore, significant increases ( p < 0.05) in ammonia-nitrogen (NH 4 -N) and DO were observed with increasing contact time, while TSS, turbidity, and NO 3 -N concentrations significantly decreased ( p < 0.05). In addition, yellow leaves and considerably lower growth rates were observed for the hydroponic plant rhizomes of P. australis , which might be an effect of light-induced fluorescein degradation due to the relatively open water surfaces of the wetlands. [ABSTRACT FROM AUTHOR]

The Living-Filter is a novel floating emergent treatment wetland design that combines a hydroponic plant-bed with curtains and baffles. Thames Water Utilities and AquaticEngineering UK designed and installed the Living-Filter in Farmoor II reservoir, Oxfordshire, UK, in July 2012. The aim is to reduce the phytoplankton biomass prior to the water treatment works intake. The plant-bed (1 m H × 21 m W × 10 m L) supports plants of Phragmites australis , Phalaris arundinacea and Carex acutiformis , with a combined system of curtains and baffles that aid the water to flow through the Living-Filter. All the water treated at the water treatment works has passed through the Living-Filter. The roots and a plastic fabric increase the surface area for biofiltration processes and the rhizosphere provides refuge for zooplankton. The research attempts to answer the question: Can the Living-Filter be used as an in-reservoir pre-treatment filtration process for reducing the phytoplankton biomass onto the water treatment works? Weekly surveys were carried out from July to October 2013 at sixteen sampling sites to measure physico-chemical and biological variables. The results for the first year of study show: (1) Soluble manganese, dissolved inorganic nitrogen and nitrites were significantly lower after treatment through the Living-Filter. (2) Chlorophyll- a removal efficiency was up to 45% during the first seven weeks. (3) Zooplankton abundance was more stable within the rhizosphere than in the water column. (4) The aerial shoots of the plants developed well, but based on root development only Phalaris and Carex should be considered for future designs. This work highlights the potential of the Living-Filter for phytoplankton reduction, but it also addresses questions that will further improve the system. [ABSTRACT FROM AUTHOR]

A pilot hybrid constructed wetland (subsurface flow line (SSL, 15 m 2 ) + floating treatment wetland line (FTWL, 90 m 2 )) treating digestate liquid fraction (DLF) in northeast Italy was monitored to determine its depuration efficiency in treating COD, total nitrogen (TN), ammonia nitrogen (NH 4 -N), nitrate nitrogen (NO 3 -N), total phosphorus (TP) and orthophosphate (PO 4 -P). CO 2 , CH 4 , and N 2 O emissions were also measured in SSL beds. The system was fed with diluted DLF (0.7 m 3 day −1 ) containing high COD (4580–6000 mg L −1 ) and TN (378.0–657.5 mg L −1 ). Removal efficiency was 57.9% for COD, 64.6% for TN, 65.1% for NH 4 -N, 35.6% for NO 3 -N, 49.2% for TP, 45.1% for PO 4 -P in SSL and of 89.2% for COD, 90.0% for TN, 89.0% for NH 4 -N, 93.8% for NO 3 -N, 50.3% for TP, 49.9% for PO 4 -P in FTWL. SSL showed a higher areal load reduction than FTWL. The carbon emitted (CO 2 -C + CH 4 -C) was always below 100% of C removed from digestate as COD, showing that during monitored periods SSL acted as C sink. The results indicate that the set-up composed by a sequence of vertical subsurface, horizontal subsurface and floating wetland represent a valid solution as secondary treatment for DLF. [ABSTRACT FROM AUTHOR]

Stormwater wet detention ponds hold a permanent pool of water and offer many beneficial uses including flood mitigation, pollution prevention, downstream erosion control, increased aesthetics, and recreational uses. Although the removal of nutrients is generally low for stormwater wet detention ponds in urban areas, floating treatment wetlands (FTWs) can be installed to offer an innovative solution toward naturally removing excess nutrients and aiding in stormwater management. To improve the stormwater reuse potential, this study assessed nutrient, microcystin, and chlorophyll-a interactions in three Florida stormwater wet detention ponds with recently implemented FTWs. Both episodic (storm events) and routine (non-storm events) sampling campaigns were carried out at the three ponds located in Ruskin, Gainesville, and Orlando. The results showed a salient negative correlation between total phosphorus and microcystin concentrations for both storm and non-storm events across all three ponds. The dominant nutrient species in correlation seemed to be total phosphorus, which correlated positively with chlorophyll-a concentrations at all ponds and sampling conditions, with the exception of Orlando non-storm events. These results showed a correlation conditional to the candidate pond and sampling conditions for microcystin and chlorophyll-a concentrations. [ABSTRACT FROM AUTHOR]

The combination of floating treatment wetland (FTW) and sediment microbial fuel cell (SMFC) has drawn increasing interest as an economical, effective, and environmentally sustainable method for energy recovery, remediation of contaminated sediments, and wastewater treatment. In this study, a novel FTW-SMFC system with vertical floating biocathodes was developed to evaluate the performance and mechanism of plants, substrates, and bio-electrochemical systems for treating low-strength surface water. Experiments were operated in batch mode and conducted in microcosms with the following six treatments: control system only containing water and sediment (CS), normal SMFC (SMFC), only plant system (PS), SMFC with plants (PSMFC), SMFC with substrates (S-SMFC), and SMFC with plants and substrates (S-PSMFC). The results show that introducing plants into SMFCs could increase the power density by 32.9–42.5%, proving that plants played an important role in enhancing bioelectricity production. The alkaline substrates reduced the cathode potential and made the cathode inefficient. The presence of plants and substrates greatly improved the removal of nitrogen and phosphorus. The removal efficiency of total nitrogen and total phosphorus increased by 8.3–27.8% and 3.5–13.9% under electrochemical treatment. There existed competition between electrochemical and plant removal approaches for nitrogen in FTW-SMFC, and electrochemical removal was prior to plant removal. Phosphorus removal was mainly through plant uptake and substrate-mediated adsorption and precipitation. The electrochemical process promoted the removal of phosphorus by enhancing the conversion of non-reactive phosphorus (NRP) to reactive phosphorus, providing 5.0–6.9% additional NRP conversion. This study furthers our understanding of the contribution and interaction of each component in the FTW-SMFC system to pollutant removal and bioenergy generation, which will contribute to the performance enhancement of FTW and further facilitate the application of FTW-SMFC technology for in-situ remediations of the polluted surface water body. • The contribution and interaction of components in FTW-SMFC were studied. • Plants enhanced the power density by 33–43% while alkaline substrates lowered it. • Increased current density promoted TN removal but limited TP removal. • Electrogenesis limited nitrogen removal by plants but raised the RP use by plants. • Electrogenesis provided 5.0–6.9% additional NRP conversion. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the feasibility of using a floating treatment wetland for removal of dissolved metals from urban runoff under full-scale conditions. The study site is a retention pond located in northeast Nantes (France) that receives the storm water runoff from a section of highway (27,000 vehicles/day, basin surface 375 m 2 ). Three floating marshes were anchored in the retention pond, each raft with a surface area of 1.5 m 2 (125 cm × 120 cm) supporting 16 plants (8 Juncus , 8 Carex ). After 4 months, plant samples were harvested, mineralized and analyzed by atomic spectrometry absorption to determine cadmium, nickel and zinc concentrations. Analysis showed Ni concentration in leaves between 23 and 31 μg/g drymatter , and between 113 and 131 μg/g in roots. Accumulation of Zn was 45–80 μg/g in leaves and 168–210 μg/g in roots. The root/leaf ratio, between 2.6 and 5.7 for Ni and Zn respectively, highlights the important function of roots in heavy metal accumulation. No cadmium accumulation was detected in plants. All three metals were also present in the biofilm on roots. Moreover, roots demonstrated a capacity to filter particulates. This study shows that floating marshes can effectively remove some metals from stormwater ponds. [ABSTRACT FROM AUTHOR]

Floating treatment wetlands (FTWs) may provide an appealing alternative to the more conventional (sub) surface flow wetlands to solve problems associated with eutrophication in urban surface waters, because they do not claim additional land area. This study examined the contribution of plant uptake to overall removal capacity of FTWs. A batch mesocosm experiment was performed during the growing season using thirty 84 L polyethylene tanks covered with 0.28 m 2 floating Styrofoam mats. Ten tanks served as a control (only Styrofoam cover), 10 tanks were planted with Iris pseudacorus , and 10 with Typha angustifolia . Nutrients were added weekly to keep total nitrogen (TN) and total phosphorous (TP) concentrations at approximately 4 mg N L −1 and 0.25 mg P L −1 . Total removal of TN an TP from the treatment with Typha was relatively low, resulting from the limited increase in plant biomass during the experiment. Total removal of TN and TP from the tanks planted with Iris was 277 mg N m −2 d −1 and 9.32 mg P m −2 d −1 during the experiment. These values were significantly higher than the values for total removal from the control tanks, i.e., 54 times higher for TN removal and 10 times higher for TP removal. Plant uptake played a major role in the removal of nitrogen and phosphorous from the water by FTWs, i.e., 74% of TN removal and 60% of TP removal resulted from Iris uptake. These results suggest that FTWs planted with Iris can be applied in a temperate climate to overcome problems with excessive algae growth in surface waters. [ABSTRACT FROM AUTHOR]

Highlights: [•] A retention pond retrofitted with a Floating Treatment Wetland was monitored. [•] A similar conventional retention pond with same inflow was monitored as a control. [•] Phosphorus plant, sediment, inlet and outlet concentrations were quantified. [•] The FTW pond showed higher total phosphorus treatment efficiency. [•] FTW increased phosphorus sedimentation while plant uptake seemed limited. [ABSTRACT FROM AUTHOR]

Abstract: A field trial comparing the fate of metals in two parallel stormwater retention ponds, one of which was retrofitted with a Floating Treatment Wetland (FTW), was carried out near Auckland, New Zealand. Results suggest that the FTW increased metal accumulation in the pond sediment especially in summer due to lower sediment Eh, more anoxic water column, neutral pH and greater source of organic matter (OM) induced by the FTW. These factors combined with higher temperature enhanced metal sorption onto OM, flocculation of particulate pollutants, metal sulphide formation and reduced OM degradation and thus limited release of metals. Unlike Zn, Cu speciation in the pond sediment was relatively unchanged under various sediment Eh conditions due to its strong binding property with sulphide and OM. Occasional moderate metal release was detected from the FTW pond sediment likely due to aerobic OM degradation at the beginning of spring and/or hydroxides reduction when sediments became reduced later in the season. No release was noticed from the conventional pond sediment likely due to biosorption and/or uptake by algae which developed in the conventional pond and settled on the bottom sediment. Direct uptake by the plants of the FTW and sorption onto root plaques are not thought to be significant removal pathways. Nevertheless roots play a major role in trapping particulate pollutants, eventually sloughing off to settle on the bottom of the pond, and provide an adequate substrate for bacterial development due to release of organic compounds which are both essential for dissolved metal sorption and metal sulphide formation. [Copyright &y& Elsevier]

Strategies for remediation of per- and polyfluoroalkyl substances (PFAS) generally prioritise highly contaminated source areas. However, the mobility of PFAS in the environment often results in extensive low-level contamination of surface waters across broad areas. Constructed Floating Wetlands (CFWs) promote the growth of plants in buoyant structures where pollutants are assimilated into plant biomass. This study examined the hydroponic growth of Juncus krausii , Baumea articulata and Phragmites australis over a 28-day period for remediation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) contaminated (0.2 µg/L to 30 µg/L) urban stormwater. With increasing PFOA and PFOS concentrations, accumulation in plant species increased although root and shoot distribution varied depending on PFAS functional group. Less PFOA than PFOS accumulated in plant roots (0.006–0.16 versus 0.008–0.68 µg/g), while more PFOA accumulated in the plant shoots (0.02–0.55 versus 0.01–0.16 µg/g) indicating translocation to upper plant portions. Phragmites australis accumulated the highest overall plant tissue concentrations of PFOA and PFOS. The NanoSIMS data demonstrated that PFAS associated with roots and shoots was absorbed and not just surface bound. These results illustrate that CFWs have the potential to be used to reduce PFAS contaminants in surface waters. [Display omitted] • Hydroponic growth of plants to remediate PFAS from stormwater were examined. • PFOA Translocation factors were found to be significantly higher compared to PFOS. • NanoSIMS data clearly demonstrate the presence of PFOA and PFOS within plant tissue. • Highest overall PFOA and PFOS removal efficacies were for Phragmites australis. • CFWs have the potential to reduce PFOA and PFOS contaminants in surface waters. [ABSTRACT FROM AUTHOR]

Highlights: [•] Develops a unique model of integrated floating treatment wetland (i-FTW) systems. [•] Model incorporates water body characteristics and FTW coverage to simulate i-FTWs. [•] A bootstrap method is used to generate predictions and estimate uncertainty. [•] First order kinetics is a simplified approach that adequately predicts performance. [•] The model fits FTW literature data (2009–2012) well. [Copyright &y& Elsevier]

Abstract: Floating treatment wetland (FTW) is one of the emerging best management practices (BMPs) for stormwater treatment where macrophytes provide a suitable root-zone environment for microorganisms that allow the plants to remove nutrients through direct uptake into their tissue. In this study, four floating mats with native Florida aquatic macrophytes were deployed in a 340m2 subtropical stormwater wet detention pond. A fountain in the pond and peat moss used to hold the substrate for plant species on the floating mats are both assumed to add nutrients to the water column. The aim of this study was to evaluate the performance of nutrient removal through the four floating mats and explore associated effects of simultaneous hydrological and biological controls related to various hydrobiogeochemical processes for nutrient removal in a multimedia pond environment. Nutrient concentrations in both inlet and outlet were monitored continuously over 13 months, with episodic (storm events) and routine (non-storm events) sampling plans carried out in parallel to justify the efficacy of the FTWs. Nutrient values within the water column and the sediment were compared before (Phase I) and after (Phase II) the deployment of the FTWs to prove the proposed hypotheses. An additional phase (Phase III) after the removal of the FTWs was added to enhance the understanding of ecosystem response. For non-storm events, phosphorus removal was substantial because of the increase in the initial concentrations, presumably due to resuspension of nutrients into the water column from the fountain operation; about 47.7% total phosphorus (TP) and 79.0% orthophosphate (OP) were removed. The removal rates of total nitrogen (TN), nitrite– and nitrate–nitrogen , and ammonia–nitrogen (NH3–N) were also calculated as 15.7, 20.6, and 51.1%, respectively. Without the uptake by plants, the nutrient removal decreased to different degrees when comparing those in non-storm events during Phase II. Considering plant species, nutrient uptake and assimilation by soft rush (Juncus effusus) was much higher than that by pickerelweed (Pontederia cordata) through both leaves and roots in this case. For soft rush, uptake rate in spring is much higher than that in fall. About 77.0gN and 8.8g P were removed from pond water via uptake and assimilation during the second phase. Despite organic nitrogen accumulation due to the pickerelweed leaf debris sedimentation, the organic nitrogen concentration in pond water was still kept at a low level, which implies that the ecosystem is capable of efficiently managing the withered plants and circulating nutrients. [Copyright &y& Elsevier]

Abstract: A field trial study with side-by-side monitoring of two parallel stormwater treatment ponds, one of which contained a floating treatment wetland (FTW), has been carried out to assess the benefit of retrofitting a conventional retention pond with a FTW. Inflow and outflow event mean concentrations (EMCs) were quantified and used to assess the overall pollutant removal efficiency of each system. Findings show that a FTW can significantly improve the runoff water quality and thus reduce the impact on the receiving environment. The present study reveals that a pond retrofit with a FTW would be more efficient than a conventional retention pond, exhibiting a 41% (for total suspended solids – TSS), 40% (for particulate zinc – PZn), 39% (for particulate copper – PCu) and 16% (for dissolved copper – DCu) lower effluent EMC. Physical entrapment of the particulate pollutants into the roots’ biofilm seems be a significant removal pathway, which could be impacted by the inflow volume. Due to higher humic content, lower dissolved oxygen and more neutral water column pH induced by the FTW, there was increased potential for adsorption processes and/or precipitation as insoluble copper sulphides, in addition to the direct Cu uptake by the plants. The dissolved zinc (DZn) inlet EMCs, which already met the Australian and New Zealand Environment Conservation Council (ANZECC) water quality guidelines and could correspond to an irreducible concentration of the system, were too low to differentiate the performance of either pond. [Copyright &y& Elsevier]

Abstract: Aquatic floating plants on BioHaven mats were tested for their potential use as a Best Management Practice to be incorporated within existing stormwater detention ponds. Plants were analyzed for their capability to remove nutrient-pollution in parallel with the study of ecological dynamics. Experiments were carried out in cylindrical mesocosms of 5m diameter and 1.2m height, above-ground pools with a water volume of 14m3. The design parameters tested were for 5% and 10% vegetated floating island coverage of the mesocosm, both with and without shoreline plants called littoral zone. This littoral shelf was 0.5m thick, graded at a downward slope of 1:5 toward the center using loamy soil with low organic matter content, excavated from below turf grass. Endemic plant species were chosen for the experimental location in central Florida based on a wetland identification manual by the Florida Department of Environmental Protection to ensure the study was not compromised by unique climate requirements of the plants. Nutrient and aquatic chemical conditions such as pH, dissolved oxygen, temperature, turbidity, and chlorophyll a were monitored to understand their relationships to the general wetland ecosystem. Real-time polymerase chain reaction analysis identified the microbial activity near the rhizospheric zone. Logistical placement considerations were made using spatial sampling across the horizontal plane of the mesocosms, beneath and around the root zone, to determine if nutrients tend to aggregate around the floating island. This study concluded that the application of floating islands as a stormwater technology can remove nutrients through plant uptake and biological activity. The most cost-effective size in the outdoor mesocosms was 5% surface area coverage of the mat. [Copyright &y& Elsevier]

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). • Flume experiment carried out with and without FTW under 3 mean flow velocities. • Flume designed as a closed loop forcing water to flow several times under the FTW mat. • Turbidity was measured over time. • FTW inclusion increased turbidity reduction by up to 45%. • Turbidity removal solely induced by a FTW was extrapolated for various pond sizes. [ABSTRACT FROM AUTHOR]

This study evaluated removal efficiencies of six contaminants of emerging concern (CECs) in floating treatment wetland (FTW) mesocosms established with either Japanese Sweetflag (Acorus gramineus Sol. ex Aiton) or canna lilies (Canna Hybrida L. 'Orange King Humbert'). The CECs included: acetaminophen (APAP), atrazine (ATZ), carbamazepine (CBZ), perfluorooctanoic acid (PFOA), sulfamethoxazole (SMX), and 17β-estradiol (E2). Each treatment was planted with different numbers of plants (i.e., 0, 10, 15, and 20), and the experiments lasted for 17 weeks. Dissipation of CECs was greater in planted treatments than in non-planted controls, and the planting number had little effect on dissipation of CECs. All residues of APAP and E2 dissipated rapidly within 2 weeks in all planted treatments. At the end of the experiment, residues of ATZ and SMX completely dissipated in the canna treatments, but not in the sweetflag treatments (75.8–87.6% and 96.3–97.1%, respectively). During the 17 week study, moderate dissipation of CBZ was observed in treatments including cannas (79.5–82.6%) and sweetflag (69.4–82.3%), while less dissipation was observed for PFOA (9.0–15.0% with sweetflag and 58.4–62.3% with cannas). Principal component analysis indicates that aqueous persistency of CECs and species of plants used influenced the dissipation of CECs in FTWs. Of the two species evaluated, canna was the most promising plant species for FTW systems designed to remove these CECs from surface water. • Floating treatment wetland (FTW) removed contaminants of emerging concern (CECs). • FTW mesocosm systems with cannas removed more CECs than sweetflags. • FTW-planting density did not influence CEC removals. • The most influential factors for CEC removals were CEC persistency and plant species. • Canna was the most promising plant species in FTW systems designed for CEC removals. [ABSTRACT FROM AUTHOR]

Floating treatment wetlands (FTW) are an emerging management practice for improving water quality in stormwater wet ponds or other detention basins. Although there is substantial evidence of nutrient reductions by FTW in mesocosm-scale studies, findings from field-scale studies on the water quality benefits of FTW are less conclusive. A medium-sized stormwater wet pond (~0.8 ha) was partially divided using an impermeable liner and monitored for 280 d using a control and FTW treatment (~20–23% FTW coverage) to determine impact of FTW on concentrations of several water quality parameters at the field-scale. Discrete samples and high-frequency, multi-point monitoring were used to assess water quality differences. No significant differences between the two treatments were found for total nitrogen, total Kjeldahl nitrogen, or total phosphorus, based on discrete samples, and in situ monitoring showed dissolved oxygen was significantly lower in the FTW treatment by roughly 2.6 mg L−1. The FTW treatment had significantly higher nitrate concentrations in discrete samples, but this finding was not supported by the high-frequency data collected when considering the full monitoring period. The FTW had significantly lower total suspended solids, based on discrete and high-frequency sampling, and resulted in a 10–43% reduction in TSS (~25% mean reduction), relative to the control. Comparison of subsets of the high-frequency data to discrete sampling data demonstrated how limited discrete sampling can lead to partial information and potentially erroneous conclusions when assessing FTW treatment effect in stormwater, especially when differences in water quality chemistry are small. Unlabelled Image • Floating treatment wetlands (FTW) were installed in a stormwater wet pond. • Discrete grab samples and high-frequency, optic measurements used for monitoring. • No significant effect of FTW on total or Kjeldahl nitrogen or total phosphorus. • Higher FTW nitrate seen in discrete sampling, but not high-frequency monitoring. • Both sampling methods showed 10–43% suspended solids reduction by FTW. [ABSTRACT FROM AUTHOR]