Nutrient uptake by constructed floating wetland plants during the construction phase of an urban residential development

Impact of water depth and flow velocity on organic matter removal and nitrogen cycling in floating constructed wetlands

The configuration of water depth (WD) and flow velocity (FV) in floating constructed wetlands (FCWs) reflects the complex interactions between hydraulic conditions and wastewater treatment performance. Properly configuring hydraulic conditions can optimize performance. This study explored the removal and degradation of organic matter and nitrogen (N) in FCWs with three different WDs (50 cm (SD), 70 cm (MD), and 95 cm (DD)) under four FV conditions (0, 0.3, 1.0, and 1.5 m/d). It also analyzed the regulatory effects of hydraulic conditions on microbial community structure to provide new insights for configuring hydraulic conditions in FCWs. The results indicate that variations in WD and FV do not significantly affect COD removal (p > 0.05), with removal efficiency (RE) consistently reaching 90 % across all conditions. However, hydraulic conditions do influence the degradation rate (k) of COD, with increased FV enhancing the k in MD and DD. In contrast, WD significantly impacts the removal of NH4+-N (p < 0.05), with RE in SD exceeding 80 % across all four FVs. The primary reason is that increased WD reduced the abundance of nitrifying bacteria (Nitrosomonas and Nitrospira) and functional genes (hao and pmoABC-amoABC). Meanwhile, increased WD and FV significantly enriched the denitrifying bacteria genera (such as Massilia, Bacillus, Ensifer, and Rhodobacter) and certain functional genes (nap and nir), favoring the denitrification process and enhancing the dissimilatory nitrate reduction to ammonium (DNRA) process. Furthermore, microbial community diversity, richness, and the number of operational taxonomic units (OTUs) were highest in SD, but decreased with increased WD. This is mainly related to changes in oxygen (O2) transmission and nutrient concentration. These findings help us understand the mechanisms by which hydraulic regulation affects the removal of organic matter and N in FCWs. They also propose potential solutions from a hydraulics perspective to enhance N removal.

Enhanced pollution removal from canal water by coupling aeration to floating treatment wetlands

Floating treatment wetlands (FTWs) are natural solutions for purifying polluted water, providing a green surface area and improving city landscape. This study investigated if the efficiency of FTWs can be improved by aeration for treating contaminated canal water. The three used plant species were Canna generalis, Phragmites australis, and Cyperus alternifolius. The experiment was carried out in three FTWs with aeration and three without aeration to compare the removal for COD, NH4+-N, E. coli, PO43--P, and Fe. In the aerated FTWs, air blowers were installed to run at two different air flow rates of 2.5 L min-1 (Batch 1) and 1.0 L min-1 (Batch 2). Aeration increased the dissolved oxygen concentrations in each tank, which came over 6.5 mg L-1 in both batches. This study sheds light on the positive impact of aeration has on COD and NH4+-N removal: these are nearly three-fold higher compared to non-aeration conditions and reached approximately 99% (1.7-log reduction) for E. coli removal. Additionally, the plant growth rate in the aerated FTWs was higher than in the non-aerated ones. The average shoot growth rate of Phragmites australis was 0.76 cm d-1 for the aerated FTW which was two-fold higher compared to the non-aerated one.

Floating treatment wetlands to improve the water quality of the Hang Bang canal, Ho Chi Minh City, Vietnam: Effect of plant species

Floating treatment wetlands (FTWs) are artificial platforms that allow aquatic emergent plants to grow in water. Aquatic macrophytes and microorganisms attached to plant roots contribute to the remediation of the contaminated water through physicochemical and biological processes. The pollutant removal treatment performance is affected by various factors, including the plant species. In this study, several plant species, i.e. Canna generalis, Phragmites australis, Pennisetum purpureum, Cyperus alternifolius rottb, Kyllinga brevifolia rottb, and Cyperus ordoratus were investigated for their potential to clean-up water from the Hang Bang canal in Ho Chi Minh City (Vietnam). Canna generalis, Phragmites australis, and Cyperus alternifolius were found to be suitable for FTWs with the highest performance compared to that of other plant species investigated. The organic and nitrogen removal rates amounted to 48-70 g COD m-3 d-1 and 0.7-1.2 g N m-3 d-1, respectively, whereas the reduction of pathogens was around 1.86-3.00 log. Furthermore, FTW systems bring other benefits such as improving ecosystem functioning and biodiversity, producing value-added products from plant biomass, as well as attracting the attention of communities, thus increasing social acceptance of environmental technology interventions.

Enhancing nitrogen removal through macrophyte harvest and installation of woodchips-based floating beds in surface-flow constructed wetlands

Wetland management maintains nitrogen (N) removal capacity in mature and overgrown constructed wetlands (CWs). We evaluated whether CW management by macrophyte harvesting, and subsequent installation of woodchips-based floating beds (WFBs) planted with Glyceria maxima and Filipendula ulmaria improved N removal. In sixteen heavily overgrown experimental CWs, we applied four treatments: i) only macrophyte harvesting, ii) 5% of the harvested-CW surface covered with WFBs, iii) 20% WFBs cover, and iv) a control treatment (heavily overgrown). N removal was determined in all wetlands at nine occasions. Plant biomass accrual, N assimilation, and denitrification genes nirS, nirK, nosZI and nosZII on plant roots and woodchips from WFBs were estimated. Macrophyte harvesting improved N removal of heavily overgrown CWs, whereas subsequent WFB installation only sometimes improved N removal. Mean N removal efficiencies (± standard deviation) overall were 41 ± 15 %, 45 ± 20 %, 46 ± 16 % and 27 ± 8.3 % for treatments i to iv, respectively. Relative biomass production, root length and root surface area for G.maxima (mean ± standard deviation: 234 ± 114 %, 40 ± 6.5 cm, 6308 ± 1059 cm2g-1, respectively) were higher than those for F. ulmaria (63 ± 86 %, 28 ± 12 cm, 3131 ± 535 cm2g-1, respectively) whereas biomass N assimilation was higher for F. ulmaria (1.8 ± 0.9 gNm-2 of WFB) than for G. maxima (1.3 ± 0.5 gNm-2 of WFB). Denitrification gene abundance was higher on plant roots than on woodchips while G. maxima hosted higher root denitrification gene abundance than F. ulmaria. We conclude that macrophyte harvesting improves N removal in heavily overgrown CWs. WFBs installation has the potential to support plant growth and denitrification in surface-flow constructed wetlands. Further studies need to evaluate the long-term effects of macrophyte harvesting and WFB installation on N removal in CWs.

Industrial wastewater treatment using floating wetlands: a review

Industrial wastewater generated from various production processes is often associated with elevated pollutant concentrations and environmental hazards, necessitating efficient treatment. Floating wetlands (FWs) have emerged as a promising and eco-friendly solution for industrial wastewater treatment, with numerous successful field applications. This article comprehensively reviews the removal mechanisms and treatment performance in the use of FWs for the treatment of diverse industrial wastewaters. Our findings highlight that the performance of FWs relies on proper plant selection, design, aeration, season and temperature, plants harvesting and disposal, and maintenance. Well-designed FWs demonstrate remarkable effectiveness in removing organic matter (COD and BOD), suspended solids, nutrients, and heavy metals from industrial wastewater. This effectiveness is attributed to the intricate physical and metabolic interactions between plants and microbial communities within FWs. A significant portion of the reported applications of FWs revolve around the treatment of textile and oily wastewater. In particular, the application reports of FWs are mainly concentrated in temperate developing countries, where FWs can serve as a feasible and cost-effective industrial wastewater treatment technology, replacing high-cost traditional technologies. Furthermore, our analysis reveals that the treatment efficiency of FWs can be significantly enhanced through strategies like bacterial inoculation, aeration, and co-plantation of specific plant species. These techniques offer promising directions for further research. To advance the field, we recommend future research efforts focus on developing novel floating materials, optimizing the selection and combination of plants and microorganisms, exploring flexible disposal methods for harvested biomass, and designing multi-functional FW systems.

Spatial distribution characteristics of denitrification functional genes and the environmental drivers in Liaohe estuary wetland

Genes nirS, nirK, and nosZ are specific for the denitrification process, which is associated with greenhouse gas N2O emission. The abundances and diversities of community containing these three genes are usually used as a common index to reflect the denitrification process, and they would be affected by differences in environmental factors caused by changes from warm to cold conditions. The quantification of denitrification in natural wetlands is complex, and straightforward identification of spatial distribution and drivers affecting the process is still developing. In this study, the bacterial communities, gene diversities, and relative abundances involved in denitrification were investigated in Liaohe Estuary Wetland. We analyzed the relative abundances, diversities, and communities of bacteria containing the three genes at warm and cold conditions using Illumina MiSeq sequencing and detected the potential environmental factors influencing their distribution by using a random forest algorithm. There are great differences in the community composition of the bacteria containing genes nirS, nirK, and nosZ. All the abundant taxa of nirS and nirK communities belonged to phylum Proteobacteria. Compared with the community composition of bacteria containing nirS and nirK, the community of bacteria containing nosZ is more diverse, and the subdivision taxa of phylum Euryarchaeota was also abundant in the community containing nosZ. The distribution characteristics of the relative abundance of nirS and nirK showed obvious differences both at warm and cold climate conditions. The oxidation-reduction potential, nitrite nitrogen, and salinity were detected as potential variables that might explain the diversity of nirS. The total nitrogen and nitrite nitrogen were the important variables for predicting the relative abundance of nirS at warm climate condition, while oxidation-reduction potential and pH contributed to the diversity of nirS at cold condition. The bulk density of sediment was detected as a potential variable affecting the relative abundance of nirK at warm and cold conditions, and diversity of nirK at warm condition, while nitrite nitrogen was detected as an important environmental factor for predicting the diversity of nirK at cold condition. Overall, our results show that the key environmental factors, which affect the relative abundance, diversity, and community of bacteria containing the functional denitrification genes, are not exactly the same, and the diversities of nirS, nirK, and nosZ have a higher environmental sensitivity than their relative abundances.

Pilot and full scale applications of floating treatment wetlands for treating diffuse pollution

Floating treatment wetlands (FTW) are nature-based solutions for the purification of open water systems such as rivers, ponds, and lakes polluted by diffuse sources as untreated or partially treated domestic wastewater and agricultural run-off. Compared with other physicochemical and biological technologies, FTW is a technology with low-cost, simple configuration, easy to operate; has a relatively high efficiency, and is energy-saving, and aesthetic. Water remediation in FTWs is supported by plant uptake and the growth of a biofilm on the water plant roots, so the selection of the macrophyte species is critical, not only to pollutant removal but also to the local ecosystem integrity, especially for full-scale implementation. The key factors such as buoyant frame/raft, plant growth support media, water depth, seasonal variation, and temperature have a considerable role in the design, operation, maintenance, and pollutant treatment performance of FTW. Harvesting is a necessary process to maintain efficient operation by limiting the re-pollution of plants in the decay phase. Furthermore, the harvested plant biomass can serve as a green source for the recovery of energy and value-added products.

Enhanced nitrogen removal from rural domestic sewage via partial nitrification-anammox in integrated vertical subsurface flow constructed wetland

This study aimed to improve the removal of nitrogen treating rural domestic sewage by developing a novel strategy for achieving partial nitrification-anammox (PNA) in an integrated vertical subsurface flow constructed wetland (VSFCW). The influent ammonia was oxidized to nitrite in the partial nitrification VSFCW (VSFCWPN), and 5 mg/L of hydroxylamine was added under the appropriate dissolved oxygen concentration level (1.2 ± 0.2 mg/L) to stabilize the average nitrite accumulation rate at 88.24% and maintain the effluent NO2--N/NH4+-N ratio at 1.26 ± 0.15. The effluent from VSFCWPN was introduced to the following chamber (VSFCWAN), where ammonia and nitrite were removed by the autotrophic anammox process. This implementation achieved high removal efficiencies for chemical oxygen demand, total nitrogen, and PO43--P, reaching 86.26%, 90.22%, and 78.94%, respectively, with influent concentrations of 120.75 mg/L, 60.02 mg/L, and 5.05 mg/L. Substrate samples were collected from 10 cm height (PN1, AN1) and 25 cm height (PN2, AN2). Microbial community analysis showed that Nitrosomonas dominated the community composition in VSFCWPN, with an increase from 1.61% in the inoculated sludgePN to 16.31% (PN1) and 12.09% (PN2). Meanwhile, Ca. Brocadia accounted for 44.81% (AN1) and 36.50% (AN2) in VSFCWAN. These results confirm the feasibility of the proposed strategy for establishing PNA and efficiently treating rural domestic sewage in an integrated VSFCW.

Computational fluid dynamics modeling of floating treatment wetland retrofitted stormwater pond: Investigation on design configurations

Floating Treatment Wetland (FTW) is a cost-effective and easy-to-retrofit device for stormwater treatment. Its treatment efficiency largely depends on the fraction of inflow entering FTW and the residence time within it. Thus hydrodynamics play a crucial role, which is affected by the design configurations of FTW and stormwater pond. Despite a spike in research on FTWs, very little is known about how various design configurations affect treatment efficiency by an FTW. Our study hypothesizes that relative positions of FTW geometry, FTW position and pond inlet-outlet have impact on the hydrodynamics and as a consequence, treatment efficiency. To explore these design features, we employed computational fluid dynamics (CFD) modeling conducted in ANSYS Fluent, validated by experimental data to examine the impact of the aforementioned design features. The results revealed that circular FTW geometry positioned near inlet coupled with center inlet-side outlet configuration achieved the highest removal (94.8%) for a non-dimensional removal rate of k_rt_HRT = 20 (k_r is the first order removal rate in per day, t_HRT is the nominal hydraulic residence time of the pond in days). Far side inlet-side outlet configuration performed the worst due to profound promotion of short-circuiting. FTW positioned near inlet performed better (61.8% mass removal on an average) than center (42.7%) and near outlet positions (54.1%) for k_rt_HRT = 20. Sensitivity analysis revealed that the treatment efficiency is most sensitive to inlet-outlet configurations. The design implications of this study will help practitioners achieving better water quality and ecological improvement goals.

Performance of constructed floating wetlands in a cold climate waste stabilization pond

Effectiveness of constructed floating wetlands (CFWs) is largely unknown for wastewater treatment in cold climates. An operational-scale CFW system was retrofitted into a municipal waste stabilization pond in Alberta, Canada. During the first year (Study I), insignificant performance was recorded for water quality parameters, although phyto-uptake of elements was evident. In Study II, doubling of the CFW area and addition of underneath aeration promoted plant uptake of elements, including nutrients and metals, following significant pollutant reduction in the water; 83 % of chemical oxygen demand, 80 % of carbonaceous biochemical oxygen demand, 67 % of total suspended solids, and 48 % of total Kjeldhal nitrogen. A mesocosm study, conducted in parallel to the pilot scale field study, confirmed the impact of both vegetation and aeration on water quality improvement. The phytoremediation potential was linked to accumulation within plant shoot and root biomass and was confirmed by mass balance. Bacterial community analyses reflected that heterotrophic nitrification, aerobic denitrification, complete denitrification, organic matter decomposition, and methylotrophy were dominant mechanisms in the CFW, likely resulting in successful transformation of organics and nutrients. CFWs appear to be a viable ecotechnology to treat municipal wastewater in Alberta; however, larger and aerated CFW systems are recommended to achieve maximum remediation. The study aligns with the United Nations Environment Program to scale up restoration of degraded ecosystems, and to improve conditions for water supply and biodiversity following recognition of 2021-2030 as the Decade on Ecosystem Restoration.

Comparative analysis of greywater pollutant removal efficiency with horizontal free water surface flow wetland with other wetland technologies

The reuse of treated wastewater for agriculture and other purposes is globally recognized as a reliable water source. Constructed wetlands are cost-effective and reliable green technologies for wastewater treatment, offering an environmentally friendly and affordable solution with minimal operational and maintenance requirements. This study assessed four wetland technologies (HFWSF, VFSF, VSSF, and HSSF) for treating greywater according to regulatory standards. The technologies effectively maintained pH levels, and both treated and untreated greywater samples met FEPA limits. They efficiently reduced dissolved and suspended particles, remaining below FEPA discharge limits for conductivity, TDS, turbidity, and TSS. However, elevated ammonia levels in both treated and untreated samples required additional treatment or mitigation. Sulphate levels were successfully mitigated, and phosphorus limits were met, with HFWSF already compliant even before treatment. Nitrate levels were reduced to meet FEPA limits, ensuring regulatory compliance. While BOD limits were met in both treated and untreated samples, untreated samples exceeded COD limits, necessitating more efficient treatment methods. HFWSF and HSSF complied with COD limits, whereas VFSF and VSSF did not. Both treated and untreated samples exceeded FEPA limits for oil and grease, indicating the need for additional treatment. Untreated samples exhibited high coliform contamination levels, underscoring the importance of effective treatment. However, all technologies successfully reduced coliform levels in treated samples, meeting FEPA limits and confirming treatment effectiveness. The combination of Typha (Domingensis) in the horizontal subsurface flow constructed wetland improved pollutant removal, nutrient removal, and contaminant elimination. Incorporating water Hyacinth (Eichhornia crassipes) with horizontal free water surface flow wetland technology demonstrated the highest efficacy in removing various pollutants. This combination outperformed other wetland technologies in effectively removing pollutants, including ammonia (60%), oil and grease (78.46%), COD (85%), TP (37.04%), FC (75%), and TC (79.59%), representing significant progress in greywater treatment.

Application of floating wetlands for the improvement of degraded urban waters: Findings from three multi-year pilot-scale installations

Floating Treatment Wetlands (FTWs) are an emerging ecological engineering technology being applied the restoration of eutrophic urban water bodies. Documented water-quality benefits of FTW include nutrient removal, transformation of pollutants, and reduction in bacterial contamination. However, translating findings from short-duration lab and mesocosm scale experiments, into sizing criteria that might be applied to field installations is not straightforward. This study presents the results of three well established (>3 years) pilot-scale (40-280 m²) FTW installations in Baltimore, Boston, and Chicago. We quantify annual phosphorus removal through harvesting of above-ground vegetation and find an average removal rate of 2 g-P m^-2_. In our own study and in a review of literature, we find limited evidence of enhanced sedimentation as a pathway for phosphorus removal. In addition to water-quality benefits, FTW planted with native species, provide valuable wetland habitat; and theoretically improve ecological function. We document efforts to quantify the local effect of FTW installations on benthic and sessile macroinvertebrates, zooplankton, bloom-forming cyanobacteria, and fish. Data from these three projects suggest that, even on a small scale, FTW produce localized changes in biotic structure that reflect improving environmental quality. This study provides a simple and defensible method for sizing FTW for nutrient removal in eutrophic waterbodies. We propose several key research pathways which would advance our understanding of the effects FTW have on the ecosystem they are deployed in.

Response of Typha domingensis Pers. in floating wetlands systems for the treatment of water polluted with phosphorus and nitrogen

The aims of this work were to evaluate the effects of P and N on the tolerance and root morphometry of Typha domingensis plants, and their implication in removal efficiency in floating treatment wetlands (FTWs). Pilot-scale plastic reactors containing plants, sediment, and tap water were arranged. FTWs consist of a plastic net, and buoyancy was provided by a PVC frame. After plant acclimation, 38 L of the synthetic effluent containing 10 mg L^-1 N + 2 mg L^-1 P was added to the reactors as follows: reactor A (with FTWs), reactor B (without FTWs), reactor BC (biological controls), and reactor CC (chemical control). Reactors were arranged in triplicate. During the experiment, three effluent dumps were made. The removals of SRP and TP were significantly higher in reactor A than in reactor B. N-NH₄⁺ removal was not significantly different between reactors A and B, while N-NO₃^- removal from water was higher in reactor A than in reactor B. At the end of the experiment, chlorophyll concentration and aerial and submerged (roots and rhizomes) biomass increased significantly in reactor A. TP concentrations were not different between rhizomes and leaves, while the lowest concentrations were observed in roots. The TKN in tissues was significantly higher in roots and rhizomes than in aerial parts. In plants exposed to the experimental solution, the internal and external root morphology changed. The use of FTWs is a promising strategy for the sustainable treatment of nutrient polluted water bodies.

Performance monitoring of constructed floating wetlands: Treating stormwater runoff during the construction phase of an urban residential development

In the context of climate change and global trend towards greenfield urbanisation, stormwater and transported pollutants are expected to increase, impairing receiving environments. Constructed floating wetlands (CFWs) can improve stormwater retention pond performance. However, performance data are currently largely restricted to mesocosm experiments, limiting design enhancement fit for field implementation. The present 12-month field study aims to fill part of these gaps by identifying limitations and necessary design improvements for CFWs on a large retention pond/lake. Water in a 2.6-ha lake receiving stormwater from a 45-ha urban area under development in subtropical Queensland, Australia, was recirculated during dry weather periods to minimise algal growth and the risks of blooms. Pollutant removal efficiencies of two full-scale CFWs were evaluated during storm events and dry weather periods as a function of inlet and outlet pollutant concentrations, flow and rainfall. Inlet TSS and TN concentrations in runoff during the construction phase of the development exceeded required water quality limits while TP inflow concentrations were low and often below the detection limit. Median pollutant load reduction efficiencies during storm-events were - 20 % TSS, -2 % TN and 22 % TP at CFW1 and 51 % TSS, 3 % TN and 17 % TP at CFW2, respectively. TSS and TN concentration removal efficiencies at CFW1 were low and highly variable, partly due to low inlet concentrations, high flow velocities and short hydraulic retention times (<1 day). However, CFW1 significantly reduced TSS concentrations during dry weather periods. In contrast, CFW2 significantly reduced TSS concentrations during both storm events and during inter-event periods. This study highlights treatment limitations associated to the operational conditions of CFWs at field-scale not identifiable in a mesocosm-scale study. Further research is necessary to investigate treatment performance of CFWs during the operational phase of the development with higher nutrient levels.

Pontederia sagittata and Cyperus papyrus contribution to carbon storage in floating treatment wetlands established in subtropical urban ponds

Carbon sequestration is considered an ecosystem service of regulation provided by diverse ecosystems, including wetlands. It has been widely evaluated in the soil of natural wetlands while in constructed wetlands, there is scanty information. In Floating Treatment Wetlands (FTW) there is none. Previously, our research group reported the efficient performance of FTW in an urban polluted pond for two years. As a follow up, the aim of this work was to investigate the contribution of Cyperus papyrus and Pontederia sagittata to carbon storage (CS) in four FTW established in eutrophic urban ponds in a subtropical region. Plant growth, productivity, and CS were assessed in the aboveground biomass of C. papyrus and P. sagittata and the belowground biomass (root mix from C. papyrus and P. sagittata), throughout 26 months in 2 FTW with an area of 17.5 m² (FTW1) and 33 m² (FTW2) and throughout 19 months in 2 FTW with an area of 25 m² (FTW3) and 33 m² (FTW4), respectively. The macrophyte growth depended on various factors, such as the season, the plant species, and the location of the FTW. High relative growth rate values were found for both species (0.125 and 0.142 d^-1 for P. sagittata and C. papyrus, respectively), especially during summer and early autumn. The highest values of productivity were 337 ± 125 g_dw m^-2d^-1 for the aboveground biomass of C. papyrus in FTW2, 311 ± 96.90 g_dwm^-2d^-1 for the aboveground of P. sagittata in FTW1, and 270 ± 107 g_dw m^-2d^-1 for the belowground biomass in FTW2. The mean values of CS for P. sagittata found in FTW1 were 1.90 ± 0.94 kg m^-2, while for C. papyrus in FTW2 they were 4.09 ± 0.73 kg m^-2. The contribution of the belowground biomass to CS was also significant in FTW2 (4.58 ± 0.59 kg m^-2).

Optimizing floating treatment wetland and retention pond design through random forest: A meta-analysis of influential variables

Floating treatment wetlands (FTWs), artificial systems constructed from buoyant mats and planted with emergent macrophytes, represent a potential retrofit to enhance the dissolved nutrient removal performance of existing retention ponds. Treatment occurs as water flows through the dense network of roots suspended in the water column, providing opportunities for pollutants to be removed via filtration, sedimentation, plant uptake, and adsorption to biofilms in the root zone. Despite several recent review articles summarizing the growing body of research on FTWs, FTW design guidance and strategies to optimize their contributions to pollutant removal from stormwater are lacking, due in part to a lack of statistical analysis on FTW performance at the field scale. A meta-analysis of eight international FTW studies was performed to investigate the influence of retention pond, catchment, and FTW design characteristics on effluent concentrations of nutrients and total suspended solids (TSS). Random forest regression, a tree-based machine learning approach, was used to model complex interactions between a suite of predictor variables to identify design strategies for both retention ponds and FTWs to enhance treatment of nutrient and sediment. Results indicate that pond design features, especially loading ratio and pond depth (which should be limited to 200:1 and 1.75 m, respectively), are most influential to effluent water quality, while the benefits of FTWs were limited to improving mitigation of phosphorus species and TSS which was primarily influenced by FTW coverage and planting density. Findings from this work inform wet retention pond and FTW design, as well as guidance on scenarios where FTW implementation is most appropriate, to improve dissolved nutrient and sediment removal in urban runoff.

Application of native plants in constructed floating wetlands as a passive remediation approach for PFAS-impacted surface water

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.

Comparative performance of Scirpus grossus for phytotreating mixed dye wastewater in batch and continuous pilot subsurface constructed wetland systems

Dye is one of the pollutants found in water bodies because of the increased growth of the textile industry. In this study, Scirpus grossus was planted inside a constructed wetland to treat mixed dye (methylene blue and methyl orange)-containing wastewater under batch and continuous modes. The plants were exposed to various concentrations (0, 50, 75, and 100 mg/L) of mixed dye for 72 days (with hydraulic retention time of 7 days for the continuous system). Biological oxygen demand, chemical oxygen demand, total organic carbon, pH, temperature, ionic content, and plant growth parameters were measured. Results showed that S. grossus can withstand all the tested dye concentrations until the end of the treatment period. Color removal efficiencies of 86, 84, and 75% were obtained in batch mode, whereas 90%, 85%, and 79% were obtained in continuous mode for 50, 75, and 100 mg/L dye concentrations, respectively. Fourier-transform infrared analysis confirmed the transformation of dye compounds after treatment and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis showed that most of the intermediate compounds were not absorbed into plants but adsorbed onto the surface of the root structure.

Practical limitations of bioaugmentation in treating heavy metal contaminated soil and role of plant growth promoting bacteria in phytoremediation as a promising alternative approach

Bioaugmentation, the addition of cultured microorganisms to enhance the currently existing microbial community, is an option to remediate contaminated areas. Several studies reported the success of the bioaugmentation method in treating heavy metal contaminated soil, but concerns related to the applicability of this method in real-scale application were raised. A comprehensive analysis of the mechanisms of heavy metal treatment by microbes (especially bacteria) and the concerns related to the possible application in the real scale were juxtaposed to show the weakness of the claim. This review proposes the use of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil. The performance of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil as well as the mechanisms of removal and interactions between plants and microbes are also discussed in detail. Bioaugmentation-assisted phytoremediation shows greater efficiencies and performs complete metal removal from soil compared with only bioaugmentation. Research related to selection of hyperaccumulator species, potential microbial species, analysis of interaction mechanisms, and potential usage of treating plant biomass after treatment are suggested as future research directions to enhance this currently proposed topic.

Long-term water quality response to increased hydraulic loadings in a field-scale free water surface constructed wetland treating domestic effluent

There is limited understanding of how constructed wetland (CW) water quality may change over time in response to increased wastewater nutrient and hydraulic loadings. We evaluated long-term water quality trends and drivers for a full-scale (8.19 ha) free water surface CW that was developed in 2001 for the treatment of increasing amounts of pre-treated domestic wastewater from the township of Mount Barker, South Australia. Water quality parameter concentrations and loads, hydraulic loadings rates, trend direction assessments (TDAs), and water quality parameter removal efficiencies were analysed over the study period. The wetland received an annual average loading rate of 947, 19644, 31039, 18140, 2985, and 807 kg year-1 for BOD5, TN, NH4-N, TKN-N, NOx-N, and TP respectively and removed on average 8%, 72%, 73%, 78%, 12% and -246% of these loadings respectively. The average influent concentrations for the study period were 2.6, 42.3, 40.6, 35.9, 9.0, and 1.9 mg L-1 for BOD5, TN, NH4-N, TKN-N, NOx-N, and TP respectively. Average concentration removal rates over the study period were 50%, 39%, 40%, 15%, -216% and -600.5% for TN, NH4-N, TKN-N, NOx-N, BOD5 and TP respectively, suggesting that nitrogen was only partly assimilated by the wetland and it was a source of organic material and phosphorus. Using seasonally and inflow rate adjusted data, TDAs predicted virtually certain increases in TN, NH4-N, and TKN-N influent concentrations over time, a decline in NOx-N, no trend in BOD5, and a possible decreasing trend in TP. The inflow explained variance accounted for approximately 50% of the variation in TN, NH4-N and TKN-N effluent concentrations. Annual removal efficiencies of N declined with increasing hydraulic loads, and hydraulic loading rates varied with management practices. Seasonal analysis showed that N removal was greater during summer and lower in winter. Due to local population growth and various management practices, hydraulic loading is variable and has often exceeded design targets. Our findings indicate the long-term performance of CWs need to be closely monitored, as water quality can deteriorate due to increased hydraulic loadings.

Review of hydraulics of Floating Treatment Islands retrofitted in waterbodies receiving stormwater

Stormwater pollution causes an excessive influx of nutrients and metals to the receiving waterbodies (stormwater ponds, lakes, and rivers), which can cause eutrophication and metal toxicity. One of the most cost-effective and eco-friendly solutions to stormwater pollution is constructing Floating Treatment Islands (FTIs) within the waterbodies receiving stormwater runoff. Treatment efficiency of FTIs depends on many factors including plant species, temperature, detention time, and pollutant loading rate. Another important factor is FTI hydraulics, which determines the amount of inflow to the root zone and residence time, greatly impacting the treatment. However, only a few studies refer to the hydraulics of waterbodies retrofitted with FTIs. This paper reviews available literature on field-scale, laboratory-scale and numerical studies on the hydraulics of FTI retrofitted waterbodies. Because of limited knowledge on the factors affecting hydraulics of waterbodies retrofitted with FTIs, current practices cannot ensure maximum hydraulic performance of this system. This review paper identifies different factors affecting the FTI hydraulics, investigates knowledge gaps, and provides future research direction for hydraulically efficient design of FTIs to treat stormwater. It was found that there is a need to investigate the impact of new design parameters such as FTI shape, FTI coverage, inlet-outlet configurations, and shape of waterbody on the hydraulic performance of FTI retrofitted waterbodies. A lack of dimensional analysis on FTI retrofitted waterbodies in existing literature revealed that field-scale values were not properly scaled down in laboratory experiments. Although a few short-circuiting prevention mechanisms (SPMs) were used in different field-scale studies, those mechanisms may be vulnerable to short-circuiting in the vertical dimension. It was revealed that studying the role of eddy diffusion and gap layer for vertical short-circuiting can help designing better SPMs. This review also identified that further investigation is required to incorporate root flexibility in the current modeling approach of FTI retrofitted waterbodies.

Efficiency and plant indication of nitrogen and phosphorus removal in constructed wetlands: A field-scale study in a frost-free area

Frost-free areas have suitable climate for wetland plant growth and constructed wetlands (CW) technology. Information on the quantification of plant biomass and uptake efficiency in field-scale CWs is limited in these climates. The removal efficiency of total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), and total suspended solids (TSS) in wastewater from sewage plants, domestic sewage, and an industrial park in 15 rural and urban CWs in Guangdong Province, China, with an average temperature of 30 °C was evaluated. The effects of influent concentration, hydraulic load, the wastewater's physicochemical properties, operating conditions, and plant uptake were analysed. The mean removal rates were 40.0%, 45.2%, 41.1%, and 71.7% for TN, TP, COD, and TSS, respectively, which were higher than the removal load of the field-scale CWs in temperate regions. Removal loads of TN, TP, COD, and TSS were highest in CWs that have been operating for 5-6 years, treating wastewater volumes of over 1 m³/m²·d. The removal efficiency was mainly related to the inflow concentration and less affected by the type of CWs. Nutrient accumulation trends were primarily linked to influent concentrations (TN: r² = 0.89, P = 0.007; TP: r² = 0.96, P = 0.001) and plant biomass (TN: r² = 0.96, P = 0.001; TP: r² = 0.92, P = 0.004). Plant biomass contributed 2%-29% and 2%-70%, respectively, to removing N and P in CWs. The average uptake concentration of N and P in aboveground plant organs (15.66 ± 4.44 mg N/g, 2.15 ± 1.18 mg P/g) was generally higher than that of other temperate plants. A strong relationship between TN and TP in the biomass was also observed; however, the relationship is only restricted by the influent TP concentration. Arundo donax is well-adapted for nutrient accumulation and adaptation and is an ideal wetland plant to purify wastewater in frost-free climates.

Macrophytes as wastewater treatment agents: Nutrient uptake and potential of produced biomass utilization toward circular economy initiatives

Macrophytes have been widely used as agents in wastewater treatment. The involvement of plants in wastewater treatment cannot be separated from wetland utilization. As one of the green technologies in wastewater treatment plants, wetland exhibits a great performance, especially in removing nutrients from wastewater before the final discharge. It involves the use of plants and consequently produces plant biomasses as treatment byproducts. The produced plant biomasses can be utilized or converted into several valuable compounds, but related information is still limited and scattered. This review summarizes wastewater's nutrient content (macro and micronutrient) that can support plant growth and the performance of constructed wetland (CW) in performing nutrient uptake by using macrophytes as treatment agents. This paper further discusses the potential of the utilization of the produced plant biomasses as bioenergy production materials, including bioethanol, biohydrogen, biogas, and biodiesel. This paper also highlights the conversion of plant biomasses into animal feed, biochar, adsorbent, and fertilizer, which may support clean production and circular economy efforts. The presented review aims to emphasize and explore the utilization of plant biomasses and their conversion into valuable products, which may solve problems related to plant biomass handling during the adoption of CW in wastewater treatment plants.

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.

Using Constructed Floating Wetlands to Remove Nutrients from a Waste Stabilization Pond

This study reports the biomass accumulation, plant nutrient concentration, and nutrient uptake rates of plants in a constructed floating wetland (CFW) installed for a sewage treatment application in Australia. Plant biomass accumulation was estimated based on field samplings throughout the duration of the study. Analysis of samples of each plant species was also completed to estimate the mean plant tissue nutrient content. The plant biomass accumulation estimate and the mean plant tissue nutrient concentration were then used to estimate the total nutrient uptake for each species. Each of the species were found to differ in biomass accumulation and plant tissue nutrient concentration and the distribution of biomass and nutrients between the shoots and roots. The nutrient uptake rates varied between the species, with B. articulata having the greatest nutrient uptake rates (shoots: N, 104 ± 31.5 g/m2, P, 12.9 ± 3.87 g/m2; roots: N, 23.9 ± 7.23 g/m2, P, 5.54 ± 1.67 g/m2). Harvesting of the four CFW islands after 375 days of growth removed an estimated 23.2 kg of N and 2.97 kg of P. The results of this study indicate that the use of CFWs with carefully selected plant species can successfully remove significant amounts of nutrients from domestic wastewater.

Assessing wetland nitrogen removal and reed (Phragmites australis) nutrient responses for the selection of optimal harvest time

Wetlands play an important role in reducing the impact of nitrogen pollution on natural aquatic environments. However, during the plant wilting period (winter) there will inevitably be a reduction in nitrogen removal from wetlands. Understanding optimum harvest time will allow the use of management practices to balance the trade-off between nitrogen removal and the sustainability of wetlands. In this study, we investigated wetland nitrogen removal and reed (Phragmites australis) nutrient responses for two years [first year: influent total nitrogen (TN) 17.6-34.7 mg L^-1; second year: influent TN 3.2-10.0 mg L^-1] to identify the optimal harvest time: before wilting, mid-wilting, or late wilting. Harvesting decreased wetland nitrogen removal in both years, with later harvest time producing a smaller decrease in TN and ammonium-nitrogen (NH₄⁺-N) removal. In addition to harvest before wilting, aboveground reed harvest at mid-wilting harvested more nutrients [carbon (C) 7.9%, nitrogen (N) 46.6% and phosphorus (P) 43.6%] in the first year, while harvest at late wilting harvested more nutrients (C 4.9%, N 7.8% and P 24.1%) in the second year, although this was not statistically significant. The late wilting harvest caused fewer disturbances to root stoichiometric homeostasis in the first year, while mid-wilting harvest promoted root nutrient availability in the second year. In addition, redundancy analysis (RDA) showed that root stoichiometry was interrelated with wetland nitrogen removal. Our results suggest that optimal harvest time was late wilting on the basis of wetland nitrogen removal, or either mid- or late wilting according to reed nutrient response to influent nitrogen concentration in some years. Our results provide crucial information for winter wetlands management.

Root growth and nutrient removal of Typha domingensis and Schoenoplectus californicus over the period of plant establishment in a constructed floating wetland

Constructed floating wetlands have been employed worldwide to treat effluents and to ameliorate water quality of water resources. However, the period of macrophyte establishment into the hydroponic functioning has not been specifically addressed. This paper reports root growth and nutrient removal of Typha domingensis and Schoenoplectus californicus in a floating structure without growth substrates over the period of 11 weeks of macrophyte establishment. The experiment was conducted in mesocosm with two replicas of each specie. Weekly batches were applied with three different concentrations of a synthetic effluent. Root growth was measured to evaluate the macrophyte adaptation. Physicochemical parameters were weekly monitored, and total nitrogen, nitrate, total phosphorus, and orthophosphate were quantified to assess nutrient removal. Both species have adapted to the floating structure, but T. domingensis presented superior root growth in relation to S. californicus. No significant differences were found during the application of first two synthetic solutions. As to solution 3, significant differences between input and output values were found to total phosphorus (F = 9.948, df = 1, p = 0.008), nitrate (F = 5.990, df = 1, p = 0.031), and total nitrogen (F = 40.212, df = 1, p < 0.0001). Removal efficiency of T. domingensis ranged from 4 to 31% for total nitrogen and from 8 to 15% for total phosphorus. S. californicus, on the other hand, varied its removal efficiency from - 6 to 5% and 2 to 12% for total nitrogen and total phosphorus, respectively. Time period of macrophyte establishment varied between species, and it was an important factor that contributed to the increase of nutrient removal rates and root growth.

Distributed treatment systems

This section presents a review of the scientific literature published in 2019 on topics relating to distributed treatment systems. This review is divided into the following sections: constituent removal, treatment technologies, planning and treatment management, and other topics. PRACTITIONER POINTS: Highlights changes and innovation in removal techniques and technologies in water treatment. Reviews management systems of distributed treatment systems. Discusses point-of-use treatment systems.

Wetlands for environmental protection

This article presents an update on the research and practical demonstration of wetland-based treatment technologies for protecting water resources and environment covering papers published in 2019. Wetland applications in wastewater treatment, stormwater management, and removal of nutrients, metals, and emerging pollutants including pathogens are highlighted. A summary of studies focusing on the effects of vegetation, wetland design and operation strategies, and process configurations and modeling, for efficient treatment of various municipal and industrial wastewaters, is included. In addition, hybrid and innovative processes with wetlands as a platform treatment technology are presented.

Floating treatment wetlands: A review and bibliometric analysis

Floating treatment wetlands (FTWs) have attained tremendous popularity for water purification purposes. Through this phyto-technology, naturally occurring macrophytes are allowed to grow on the water surface on a buoyant raft or a rigid support, keeping the plant roots permanently in contact with the water and removing pollutants via several processes. The objective of this study was to review studies that have developed FTWs and to perform a bibliometric analysis using three keywords: "Floating", "Treatment" and "Wetlands". From bibliometric analysis using VOSviewer software and the Web of Science database, it was possible to verify the number of publications over the years and the countries and authors with the most published articles on these systems and other related terms. Subsequently, a review was performed on the main mechanisms of pollutant removal by FTWs as well as experiences and recommendations for major design and operating aspects for their application, such as water depth, hydraulic retention time (HRT), floating mat, water surface coverage, artificial aeration, plant selection and pruning or harvesting. It was verified that FTWs are a potential technology for treating several wastewater types and water remediation under different conditions. Even with the increasing number of publications in recent years, many design and operation aspects related to system performance still demand more research in order to better understand the relations between macrophytes and other pollutant removal mechanisms and to thereby improve the treatment efficiency of FTW systems.

Rapid plant responses following relocation of a constructed floating wetland from a construction site into an urban stormwater retention pond

This study compared plant growth, nutrient partitioning and total nutrient uptake by tall sedge (Carex appressa) plants in large-scale Constructed Floating Wetlands (CFWs). Two CFWs with a total area of 2088 m² were installed in a 2.6 ha man-made urban lake to treat stormwater runoff during the construction phase of a 45-ha residential development. After 12 months of operation, parts of the CFWs, with a total area of 147 m², were removed from the urban lake and relocated into a well-established 0.127-ha stormwater retention pond at another site. Biomass and nutrient concentrations of C. appressa shoots above the floating mat and roots below the mat were analysed at both sites 12, 16 and 25 months after initial planting. Plants at the urban lake maintained an extensive root network but there was no increase in total plant biomass at 16 and 25 months after planting. In contrast, the relocated plants in the stormwater pond showed extensive shoot growth but a significant decline in root biomass. C. appressa at the urban lake removed and sequestered 1.00 ± 1.04 g m^-2 N, 0.11 ± 0.07 g m^-2 P and 1.03 ± 0.81 g m^-2 K while plants at the pond removed 11.20 ± 2.29 g m^-2 N, 1.37 ± 0.26 g m^-2 P and 16.13 ± 2.88 g m^-2 K during 12 and 25 months after planting. This study demonstrated that C. appressa adapted rapidly to changes in nutrient availability. The implications are interesting as nutrient levels can be low in constructed lakes during the initial phase of urban developments but can increase rapidly as the development progresses. The study demonstrated multiple benefits of CFWs for stormwater treatment during the early construction stages of an urban development and the potential benefits of relocating and establishing CFWs in existing stormwater retention ponds and lakes.

Development and evaluation of a process-based model to assess nutrient removal in floating treatment wetlands

Modelling is a useful tool for comprehensively describing the processes occurring in floating treatment wetlands (FTWs). However, temperature effects and phosphorus dynamics are not considered in the current FTW models. Therefore, a process-based model comprised of a plant growth submodel, a nitrogen dynamic submodel and a phosphorus dynamic submodel was developed to understand the complicated processes occurring in FTWs. The model was fully calibrated using a mesocosm FTW system operated for 168 days. Global sensitivity analysis revealed that nitrogen removal performance was predominantly sensitive to parameters representing plant characteristics and microbial activity. Because of the high concentration of organic matter, mineralization and sedimentation played important roles in nitrogen and phosphorus removal. In addition, the coprecipitation rate of phosphate also had a significant influence on phosphorus removal performance. When further investigation was applied to understand the behavior of the model, the ratio of nitrogen to phosphorus in plant tissue was found to be an indicator of the nutrient limitation in the water column. Furthermore, the model illustrated that both FTW operating conditions and plant characteristic parameters exerted an important influence on nitrogen removal and plant uptake contribution. Therefore, the selection of appropriate operating conditions and plant species can achieve high nutrients removal and make effective use of plants in FTWs. The model provides a useful tool for assessing the nutrients removal performance of FTWs and for evaluating strategies for them in design and operation.