Floating Treatment Wetlands System Research Articles

Development of Bacterial Augmented Floating Treatment Wetlands System (FTWs) for Eco-Friendly Degradation of Malachite Green Dye in Water

Industrial revolution has intensified water pollution due to the indiscriminate discharge of untreated industrial effluents into water bodies, posing a serious threat to the whole ecosystem. Recently, the floating treatment wetlands system (FTWs) technique has been used as one of the most innovative, cost-effective and environment-friendly option for wastewater treatment. The present study is aimed at investigating the Malachite green (MG) dye decolorizing potential of Eichhornia crassipes (water hyacinth) through the development of a bacterial augmented FTWs. To an artificial FTWs, vegetated with E. crassipes and bioaugmented with Pseudomonas putida and Pseudomonas sp., synthetically prepared MG dye enriched wastewater was added. Among all the treatments developed, floating wetlands treatment T2 (consisting of dye, E. crassipes and Pseudomonas putida) performed the best in decolorizing the dye and in reducing values of electrical conductivity (EC), pH and total dissolved solids (TDS) of the treated water. Bacterial inoculation proved fruitful in assisting the increased MG dye decolorization in partnership with E. crassipes and also helped in aquatic plant growth promotion. MG dye toxicity effects were studied through phytotoxicity assay using FTWs treated water on Pisum sativum seeds, and satisfactory results were obtained. From experimental results, it can be seen that Eichhornia crassipes with bacterial inoculation have a strong ability to degrade and decolorize MG dye in textile effluents. We conclude that the plant-microbial assisted FTWs technique can be a unique approach to remediate the textile dye effluents before their release into water bodies.

Textile Wastewater Treatment Through Plant–Microbe Synergism in a Floating Treatment Wetland System

Textile wastewater treatment is a complex process that requires a range of chemicals and generates hazardous sludge. This article evaluates a chemical-free, floating treatment wetlands system for the treatment of textile wastewater containing reactive red and reactive yellow dyes. Two aquatic plants, Eichhornia crassipes Solms and Pistia stratiotes L., were selected and vegetated in the system. The efficacy of the system was enhanced by inoculation of two pollutant-degrading and plant growth-promoting bacteria: Bacillus cereus and Bacillus subtilis. The eight treatments were designed with different combinations of plants and bacteria. The performance of the system was evaluated through key parameters of electrical conductivity, total dissolved solid, total suspended solids, biological oxygen demand, chemical oxygen demand, and dye concentration for the treated wastewater. The best treatment achieved the optimized plant–bacteria synergism and exhibited good reductions in the physicochemical parameters and the values of all the wastewater parameters were within the limits set in the standards of National Environmental Quality Standards and Zero Discharge of Hazardous Chemicals Program.

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

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

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

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

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

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

Enhanced dissipation of trace level organic contaminants by floating treatment wetlands established with two macrophyte species: A mesocosm study

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.

Alkalinity of Irrigation Return Water Influences Nutrient Removal Efficacy of Floating Treatment Wetland Systems1

Abstract Water quality concerns often prevent reuse of captured irrigation return water for irrigation of specialty crops. Prior research indicated alkalinity of specialty crop operation irrigation varies from 0 to >500 mg.L−1 ( >0.06 oz.gal−1) CaCO3 across the United States. Floating treatment wetlands (FTWs) are an option for remediation of nutrients in irrigation return water, but effects of variable alkalinity on nutrient removal efficiency of FTWs are unknown. An experimental FTW system was developed to quantify the effect of alkalinity on the growth and nutrient uptake capacity of three plant species. ‘Rising Sun' Japanese iris (Iris ensata ‘Rising Sun’ Thunb.), upright sedge (Carex stricta Lam.);, and switchgrass (Panicum virgatum L.). were grown for 6 weeks at one of five alkalinity treatment levels, representing the alkalinity range of nursery and greenhouse irrigation runoff: 0, 100, 200, 300, and 400 mg.L−1 CaCO3 (0, 0.01, 0.02, 0.04, 0.05 oz.gal−1 CaCO3). Overall, Japanese iris demonstrated consistent remediation across each alkalinity treatment for both nutrient load reduction and plant accumulation. Species of iris warrant greater consideration and use in bioremediation systems. Both upright sedge and switchgrass could be used in systems with appropriate alkalinity levels. Future work should consider assessing novel plants at different points within their growth cycle, extended exposure durations, and decreased hydraulic retention time. Index words: Aquatic plant, nitrogen, phosphorus, sodium bicarbonate, nitrogen speciation. Species Used in this study: ‘Rising Sun' Japanese iris (Iris ensata ‘Rising Sun' Thunb.); upright sedge (tussock sedge) (Carex stricta Lam.); switchgrass (Panicum virgatum L.).

Implementation of Floating Treatment Wetlands for Textile Wastewater Management: A Review

The textile industry is one of the most chemically intensive industries, and its wastewater is comprised of harmful dyes, pigments, dissolved/suspended solids, and heavy metals. The treatment of textile wastewater has become a necessary task before discharge into the environment. The textile effluent can be treated by conventional methods, however, the limitations of these techniques are high cost, incomplete removal, and production of concentrated sludge. This review illustrates recent knowledge about the application of floating treatment wetlands (FTWs) for remediation of textile wastewater. The FTWs system is a potential alternative technology for textile wastewater treatment. FTWs efficiently removed the dyes, pigments, organic matter, nutrients, heavy metals, and other pollutants from the textile effluent. Plants and bacteria are essential components of FTWs, which contribute to the pollutant removal process through their physical effects and metabolic process. Plants species with extensive roots structure and large biomass are recommended for vegetation on floating mats. The pollutant removal efficiency can be enhanced by the right selection of plants, managing plant coverage, improving aeration, and inoculation by specific bacterial strains. The proper installation and maintenance practices can further enhance the efficiency, sustainability, and aesthetic value of the FTWs. Further research is suggested to develop guidelines for the selection of right plants and bacterial strains for the efficient remediation of textile effluent by FTWs at large scales.

Phytoplankton composition and abundance in the floating treatment wetlands (FTWs) system of Lake Maninjau, Indonesia

Algae blooms have been recorded several times in Lake Maninjau and recently in April 2018. Floating treatment wetlands (FTWs) system was installed in June 2018 in Lake Maninjau as one of the methods to reduce the risk of eutrophication in this lake. The study is to reveal the characteristics of phytoplankton composition and abundance including environmental conditions in the FTWs system in Lake Maninjau. TP concentrations tend to decrease due to nutrient dynamics such as the dilution effect of precipitation which shifting the dominant of phytoplankton composition during observation. There were two different groups separating phytoplankton composition between the inside and outside of the FTWs system. The dominant species of Aphanizomenongracile and Synedra ulnawere related to high conductivity and the TP concentration while Oscillatoriaformosa was related to the high temperature. Phytoplankton abundanceon the inside of FTWsdecreased over time compared to the outside of FTWs, while chlorophyll-a fluctuated with the average value of 6.79 µg.L−1 on the inside of FTWs and 9.54 µg.L−1 on the outside of FTWs. This study suggests that the FTWs could potentially reduce the chlorophyll-a thereby minimizing the risk of eutrophication in a tropical lake.

Reusable biopolymer based heavy metal filter as plant protection for phytoremediation

Bioremediation via floating treatment wetlands/islands (FTW/I) is a sustainable, upcoming strategy to clean over-fertilized waters. Heavy metal pollution could be addressed in the same system. For implementing this feature, heavy-metal-adsorbing filter papers were prepared in a scalable procedure. Polyamine-functionalized papers based on the grafting of polyethyleneimine (PEI) and chitosan were prepared in aqueous immersion baths and tested for their heavy metal adsorption capability. Compared to untreated cellulose, the prepared filter papers exhibited great heavy metal reduction in a filtration setup. Compellingly, the natural biopolymer functionalization with chitosan adsorbed similar or even higher amounts (80% Ni, 65% Co, 100% Cu, 85% Fe, 40% Cr, 90% Cd, and 66% Zn of the 5 ppm heavy metal sulfate solutions) compared to the PEI filters (48% Ni, 36% Co, 89% Cu, 96% Fe, 45% Cr, 84% Cd, and 62% Zn) at pH 6.5. Moreover, the filters can be re-used simply by acidic washing to desorb the heavy metals, which was demonstrated in five repeating cycles. The presented chitosan–cellulose papers were prepared from renewable resources in a 3-step production lane and are a sustainable choice for various heavy-metal-removing applications. The papers can be implemented into floating treatment wetland systems to protect plants and microorganisms during phytoremediation processes and to add the additional feature of heavy metal removal for FTWs. • The chitosan filter papers exhibit efficient heavy metal adsorption. • They were implemented into a natural FTW/I vetiver grass set up. • The filter papers can be re-used after acidic washing with citric acid. • The batch synthesis is highly scalable & transferable to reel-to-reel production.

Degradation of Nitrate, Ammonium and Phosphate in Domestic Wastewater by Aquatic Plants, Actinoscirpus grossus in Floating Treatment Wetland System (FTWs)

Ecological technologies such as wetlands constructed for wastewater treatment are innovative solutions for environmental protection and restoration. This study examines a Floating Treatment Wetlands System (FTWs), which is a new treating concept using macrophytes rooted in modified growing aquatic plants with floating systems. An aquatic plant, Actinoscirpus grossus obtained from rice fields in Banda Aceh. FCWs filled with five plants per shoot with five compartments were fed with domestic wastewater with a flow rate of 7 L/hour. Plant height was varied by 90cm - 150cm in Pond 1 and 50cm - 90cm in Pond 2, and Pond 3 was prepared as a control (without plants). Water quality in influent and effluent was analyzed every two weeks with a duration of 18 weeks and nine times sampling. Results showed a decrease in the concentration of nitrate, ammonium, and phosphate in the effluent flow with degradation efficiency (% DE) on average, NO3-N: 76.34%; NH4-N: 97.75%; and PO4 3-: 89.45%; respectively. The degradation of domestic wastewater showed very significant results. The periodic harvest management process becomes an important part of aquatic plants, Actinoscirpus grossus to achieve optimum results in treating waste, i.e., for 112 days with a maximum plant growth height of 165cm and 173cm for both variations of experimental ponds.

Evaluation of Plant Structure in Urban Lake Ecosystem and Their Performance in Treatment Wetland Systems (TWS) to Maintain Lake Water Quality in Megacity Jakarta, Indonesia

Urban lakes have become important city landscape to help maintaining the balance of hydrology (groundwater and surface) and ecology in urban ecosystem. Due to experiencing encroachment and severe pollution problems, the lakes require urgent handling and management. One of the promising alternative solutions of lake restoration and management is applying ecosystem-based approaches and/or green technology such as treatment wetland systems using plants. This paper will review various types of tropical plants (terrestrial and aquatic plants) and evaluate their role in maintaining urban lake water quality in megacity Jakarta and their performance in treatment wetland systems from our previous and on-going studies. Plants with more important role to contribute to improve lake water quality are the submerged and emergent plants. The most common and robust types of aquatic plants in less abundance and balanced plant structure and composition at the lake shoreline and littoral area with controlled submerged plants and no indication of invasive species give better lake water quality of urban lakes. The most robust type of aquatic plants and few types of terrestrial plants studied could give significant nutrient and solids removal efficiency in both constructed and floating treatment wetland systems. Using plants with ecosystem-based approaches according to plant structure at the lake surroundings and in the treatment wetland systems could contribute to maintain better urban lake water quality.

Runoff pH Influences Nutrient Removal Efficacy of Floating Treatment Wetland Systems

Floating treatment wetlands (FTWs), a modified constructed wetland technology, can be deployed in ponds for the treatment of nursery and greenhouse irrigation runoff. The pH of nursery and greenhouse operation irrigation water varies from 3.3 to 10.4 across the United States. Water flow rate, plant species selection, and variable nutrient inputs influence the remediation efficacy of FTWs and may interact with the pH of inflow water to change nutrient remediation dynamics. Therefore, an experiment was designed to quantify the effect of pH on the growth and nutrient uptake capacity of three macrophyte species using a mesocosm FTW system. ‘Rising Sun’ japanese iris (Iris ensata), bushy bluestem (Andropogon glomeratus), and maidencane (Panicum hemitomon) were grown for two 6-week periods and exposed to five pH treatment levels representing the range of nursery and greenhouse irrigation runoff, 4.5, 5.5, 6.5, 7.2, and 8.5, for a total of 15 plant and pH combinations. Water was treated with either hydrochloric acid to decrease the pH or sodium hydroxide to increase the pH. The pH-adjusted solutions were mixed with 12 mg·L−1 nitrogen (N) and 6 mg·L−1 phosphorus (P) fertilizer (64.8 g·m−3 N and 32.4 g·m−3 P). Differences in pH impacted both N and P removal from the FTW systems for two of the three species studied, maidencane and bushy bluestem. Higher pH treatments reduced nutrient removal efficacy, but plants were still capable of consistently removing nutrients across all pH treatments. Conversely, ‘Rising Sun’ japanese iris maintained similar remediation efficacies and removal rates across all pH treatments for both N and P, possibly due to the ability to acidify its rhizosphere and modify the pH of the system. Average N and P loads were reduced by 47.3 g·m−3 N (70%) and 16.6 g·m−3 P (56%). ‘Rising Sun’ japanese iris is a promising plant for use in highly variable conditions when the pH of irrigation runoff is outside the typical range (5.5–7.5). Results from model simulations poorly predict the nutrient availability of P and ammonium in effluent, most likely due to the inability to determine plant and biological contributions to the system, such as N-fixing bacteria.

Comparing the performance of four macrophytes in bacterial assisted floating treatment wetlands for the removal of trace metals (Fe, Mn, Ni, Pb, and Cr) from polluted river water.

Here we compared the performance of four macrophytes namely Brachia mutica, Typha domingensis, Phragmites australis and Leptochala fusca, in bacterially assisted floating treatment wetlands (FTWs) for the clean-up of five trace metals (Fe, Mn, Ni, Pb, and Cr) from polluted river water. The river water was artificially spiked with reagent grade chemicals to increase the trace metal pollution. The macrophytes were planted in a polystyrene sheet to prepare FTWs, which were placed over the metal-contaminated river water. The consortium of five rhizospheric and endophytic bacterial strains, i.e., Aeromonas salmonicida, Pseudomonas indoloxydans, Bacillus cerus, Pseudomonas gessardii, and Rhodococcus sp., was inoculated support the natural remediation ability. We found a significant reduction in the metal content by all four macrophytes and the removal was significantly enhanced when bacterial inoculum was applied. The maximum removal was observed in FTWs planted with P.australis and inoculated with bacteria. In this treatment (T6) the Fe, Mn, Ni, Pb and Cr contents were reduced to 0.53, 0.20, 0.09, 1.04 and 0.07 mg L-1 after five weeks retention time. The bacterial inoculation sufficiently increased the plant biomass. All macrophytes depicted potential to uptake and translocate trace metals in the roots instead of shoots. The bacterial inoculation acclimatize the plants roots followed by shoots and enhanced the uptake of metals by macrophytes. This study emphasized the usefulness of macrophytes-bacteria mutualism in FTWs system for the remediation of trace metals. The similar systems may provide practical solutions for the remediation of trace metals of polluted river water.

TREATMENT OF TEXTILEWASTEWATER USING MICROBES’ INOCULATED FREE-FLOATINGAQUATICPLANTSBASED WETLANDS

Textile wastewater is a big source of aquatic and environmental pollution. Currently, various physicochemical textile effluent treatments are practiced in the textile industry, but they have challenges with respect to cost, maintenance, labour management, chemicals usage and production of additional sludge. The present study was carried out to develop a less expensive, chemical- free, green and sustainable plant based floating treatment wetlands (FTWs) system augmented with bacteria to remedy the effluents from textile finishing unit. Two free-floating aquatic plants, Eichhornia crassipes and Pistia stratiotes, were vegetated to develop FTWs system and its efficacy was studied with and without inoculating two plant growth-promoting and pollutant- degrading bacteria, Bacillus cereus and Bacillus subtilis. The worth of this system was analyzed by screening physicochemical parameters like potential hydrogen (pH), electric conductivity (EC), total dissolved solids (TDS), total suspended solids (TSS), biological oxygen demand (BOD) and chemical oxygen demand (COD) of wastewater for hydraulic retention periods of 0, 24, 48 and 72 hours. The pH of the treated wastewaters was changed from acidic to neutral/alkaline side while a significant reduction was found in all other physiochemical parameters as per set limits of industrial and municipal wastewater standards as specified by the National Environmental Quality Standards (NEQS) of Pak istan and Zero Discharge of Hazardous Chemicals (ZDHC) program.

Application of floating treatment wetlands in a highly eutrophic lake, Indonesia: a new tool for lake restoration and provision of microhabitat

Two sets of floating treatment wetlands (FTWs) have been evaluated as a tool for lake restoration and microhabitat provision for aquatic biota in a highly eutrophic and polymictic Lake Maninjau, Indonesia. Each FTW system consisted of 14 units square floating frame built using PVC pipes and palm sugar fibres as material mat transplanted onto net. All units of FTW were planted with different vegetation composition arrangement then placed inside the square metal frame attached on buoyant plastic drums to support the FTWs against the wave. The plants used in this study were Canna variegata, Vetiveria zizanioides, Cyperus papyrus, Echinodorus polaefolius and Limnocharis flava. FTWs were evaluated for 7 months for nutrient removal efficiency and other water quality indicators. Despite unstable lake conditions accompanied by strong waves and lake mixing, the cage and the PVC frame of FTWs applied remained intact and providing the buoyancy to support the plant growth. The plants in FTWs grew and adapted well in the turbulence water and even in the hypoxic conditions. Improvement of lake water quality in the FTWs area may be small but the accumulated nutrients content in the plant shoots suggests high removal of nutrients. In total by the end of observation, one FTWs system could remove > 100 g N and > 7 g P from the lake water. During field observation, important local fish and diverse wildlife activities were recorded including inhabiting, foraging, breeding, nursing and resting in the FTWs. Our study suggests that FTWs can be a promising tool for lake restoration to improve lake water quality and for microhabitat provision.

Floating treatment wetlands supplemented with aeration and biofilm attachment surfaces for efficient domestic wastewater treatment

Floating Treatment Wetlands (FTWs), comprising a floating matrix or framework vegetated with emergent wetland plants whose roots extend into the water below, have potential for treatment of wastewaters. Low oxygen concentrations beneath FTWs and wash-out of microbial communities can limit decomposition of organic matter and nitrification of ammonium-N in domestic wastewaters. This study aimed to test the utility of two different configurations of FTWs supplemented with mechanically aerated Biofilm Attachment Surfaces (BAS) to provide post-primary treatment of domestic wastewater. Two pilot-scale FTW treatment trains were developed at a domestic wastewater treatment plant in Hamilton, New Zealand using ten 1 m3 volume tanks, with 1 m2 square floating mats planted with Carex virgata. These were: (1) a single-pass (direct flow-through) system comprising an aerated FTW tank with subsurface BAS followed by four non-aerated FTW tanks in series, where (endogenous carbon inputs from wetland plants, along with organic carbon from the wastewater would promote denitrification; and (2) a recirculating system incorporating a pre-anoxic phase settling tank with FTW and BAS, followed by an aerated FTW tank with BAS from which 4/5 of the outflow was recirculated back to the initial anoxic stage where the (endogenous) organic matter in the incoming wastewater would provide the primary source of carbon to promote denitrification. The remaining 1/5 flowed into three non-aerated FTWs in series. Performance of each treatment stage was monitored monthly for one year from February 2015 to January 2016 for organic matter (BOD5: Biochemical Oxygen Demand; TSS: Total Suspended Solids), nutrients (nitrogen and phosphorus) and E. coli removal. The single-pass system had almost complete removal of both TSS and cBOD5 with >93%, maintaining the final effluent TSS and cBOD5 concentrations at below 5 and 4 mg L−1 respectively. The single-pass system had a lower NH4-N reduction (4.9 g m−2 d−1) compared with that in the recirculating system (6.9 g m−2 d−1), but achieved higher denitrification (1.7 g m−2 d−1) than that in the recirculating system (1.4 g m−2 d−1) as more organic carbon from the inflow wastewater was available in the single-pass system for denitrification. The recirculating FTW system achieved slightly higher removal of Total-P (TP: 44.9%) and Dissolved Reactive Phosphorus (DRP: 29.7%) than those in the single pass FTW system (TP: 36.7%; DRP: 24.3%), and both systems had a similar ~3-log E. coli reduction (from 106 to 103 MPN 100 ml−1) during the one-year experimental period. This one-year pilot-scale FTW study showed that FTWs supplemented with mechanically aerated BAS could be a practically option to retrofit existing waste stabilisation ponds to enhance organic matter, nitrogen and E. coli reduction. Furthermore, they may have some potential advantages over other types of intensified constructed wetlands, since they don’t need costly graded gravel (or other solid media), provide ready access to aeration diffusers for maintenance purposes, have low susceptibility to clogging, and can be more readily de-sludged if required.

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.

Remediation of acid mine drainage-impacted water by vetiver grass (Chrysopogon zizanioides): A multiscale long-term study

Acid mine drainage (AMD) is an acidic discharge from mining sites that contains elevated levels of metals and sulfate (SO42−). AMD can inflict health and environmental dangers through metal toxicity and physical stress. Current methods for AMD treatment, including chemical or passive biological treatments, are often non-sustainable owing to expense, require continuous maintenance, or are unsuitable for prolonged treatment. Our ultimate goal is to develop a cost efficient and sustainable floating treatment wetland system using vetiver grass (Chrysopogon zizanioides). Year-long large- and small-scale hydroponic experiments were used to determine the effectiveness of vetiver for treating AMD-impacted waters from the Tab-Simco mine site in southern Illinois. For the large-scale mesocosmic study, vetiver rafts were suspended in 100-gallon containers. Water quality was monitored by chemical analysis of samples every 28 days and at the end of the experiment (364 days); plant health was monitored by measuring changes in biomass and recording visual changes in root and shoot coloration and morphology. There was higher net removal of Fe (81%) and Pb (81%) with lower removal of Ni (38%), Zn (35%), SO42− (28%), Mn (27%), Cr (21%), Al (11%) and Cu (8.0%). Metals were mainly localized on the root surface as Fe plaques, whereas Mn and Zn showed greater translocation from root to shoot. Furthermore, toxicity characteristic leaching procedure showed that vetiver biomass was not hazardous waste as a result of metal accumulation. From the small-scale experiment, there was near complete removal of SO42− (91%) and metals (90–100%) with the exception of Pb (15%) and Cu (0.0%). These experiments demonstrate that vetiver can effectively remediate AMD-impacted waters over an extended period of time.

Aeration and plant coverage influence floating treatment wetland remediation efficacy

Nutrient contamination of waterways is a growing concern, instigating the emergence of floating treatment wetland systems (FTWs) to remove nutrients from water. To determine if aeration of water systems enhances nutrient removal efficacy or nutrient fixation within plant tissues, aeration in combination with FTW installation techniques were investigated. During two separate trials with Juncus effusus and Canna flaccida, treatments consisted of either aerated or non-aerated mesocosms, with varying coverage and planting density combinations. Aeration increased the dissolved oxygen levels within each mesocosm, but reduced the removal of nitrogen and phosphorus from the water column in comparison to non-aerated systems. Plant samples collected from 100% planting density treatments that were aerated had a greater nitrogen uptake than non-aerated by as much as 55% or 13.5 g/m2 at harvest. Some discrepancies between plant uptake and water column nutrient levels can be attributed to microbially-mediated nitrogen losses (e.g., denitrification).