Wetland Treatment System Research Articles

Hurricane and seasonal effects on hydrology and water quality of a subtropical urban stormwater wetland

Understanding the hydrology of a created or restored wetland is a critical component in understanding the overall functioning of its design, and in determining if the original goals of the wetland are being met. Freedom Park, a 20-ha park constructed in Naples, Florida in 2009, includes a 4.6-ha subtropical stormwater wetland treatment system for improving the water quality of the downstream impaired Gordon River and estuaries that flow into the Gulf of Mexico. Subtropical wetlands often present significant issues of sustaining viable wetland vegetation communities because of long wet and then long dry patterns in the wetlands’ hydroperiods. The treatment wetland’s watershed includes 1766 ha of an urbanized Naples metro area. The goals of the stormwater wetlands are to improve the water quality, reduce peak flows discharging into Gordon River and further to Naples Bay, and provide an aesthetic water park for the public. A monthly hydrologic budget for the period August 1, 2016 to January 31, 2018 showed the following averages: pumped surface water inflow of 50.1 cm week−1; average surface outflow of 38.8 cm week−1; precipitation of 3.76 cm week−1, potential evapotranspiration (PET) of 5.34 cm week−1; and estimated seepage of 14.8 cm week−1. During the wet season, water pathways are largely influenced by pumped surface inflow and surface outflow, balanced to not produce significant changes in water level from month to month. Groundwater seepage and evapotranspiration are the most important outflows during the dry season. A stormwater pulsing study during Hurricane Irma (September 10, 2017) showed that after an initial inflow flush due primarily to rainfall, total phosphorus and total nitrogen concentrations were higher at the outflow than at the inflow for several days during and immediately after the hurricane. Similarly, the mass of nutrients leaving the system was 130% and 37% higher for TN and TP, respectively, than the mass entering the system during this 6-day period during and immediately after the hurricane. Ironically, the design of the pump-only inflow did not allow for major urban runoff during the hurricane to enter the wetlands. Samples taken at the inflow and outflow of the system for four other storm events throughout the 2017 wet season (July through October) were also analyzed for their effects on water quality. While total phosphorus removal during and after storm events is comparable to normal conditions at the Freedom Park wetlands and other stormwater treatment wetlands in the world, total nitrogen removal decreased during and after storm events.

Simulation of Constructed Wetland in treating Wastewater using Fuzzy Logic Technique

Constructed wetlands act as a natural alternative to conventional methods of wastewater treatment. CW are found effective in wastewater containing inorganic matter, organic matter, toxic compounds, metals, nitrogen, phosphorous, heavy metals, organic chemicals, and pathogens. The treatment efficiency by the adaptation of CWs in treatment process is achieved by a complex interaction between plants, microorganisms, soil matrix and substances in the wastewater. Constructed wetland treatment systems are engineered systems designed in such a manner that it could take advantages of those processes occurring in natural wetlands in treating the wastewater concerned, but in a more controlled environment. Petrochemical wastewater was the type of wastewater taken for the study. Characteristics of petrochemical wastewater mainly oil, Biological Oxygen Demand (BOD) and Chemical oxygen demand (COD) were selected for treatment in constructed wetland as they are predominant in petrochemical wastewater. The conventional methods followed in the treatment are chemical and biological treatment. In this study, a fuzzy model for water quality assessment has been developed and water quality index value was obtained. The experiment conducted and further analysis using fuzzy logic indicated that interpretation of certain imprecise data can be improved within fuzzy inference system (FIS). Based on the analysis, we could observe that Typha sp contained wetland cell showed greater efficiency in removal of parameters such as COD and BOD than Phragmites sp. wetland cell.

Treatment of oil sands process-affected waters using a pilot-scale hybrid constructed wetland

Constructed wetland treatment systems (CWTSs) could provide a passive, low-energy strategy for mitigating risks associated with oil sands process-affected waters (OSPWs). Due to the large volumes (over 975 million m3), heterogeneous composition, and acute and chronic toxicity of OSPW, passive and efficient treatment to decrease risks to biota will be necessary once operators obtain regulatory permission to discharge into aquatic receiving systems. The research objective was to design, assemble, and measure performance of a pilot-scale hybrid CWTS for treatment of OSPW. Constituents of concern (COCs) identified in OSPW included NAs, oil and grease, As, B, Cu, Pb, and Zn. Oxidizing conditions (net sediment redox > −50 mV) were promoted to allow aerobic degradation of organic constituents, and co-precipitation of arsenic with iron oxyhydroxides. Treatment of Cu, Pb, and Zn was targeted through precipitation with sulfides in reducing “micro-environments” in wetland sediments. Solar photocatalytic reactors (hybrid components) were used to remove recalcitrant organics. Performance was assessed using rates and extents of removal of COCs and changes in toxicity as indicated by Ceriodaphnia dubia. Mean total naphthenic acid fraction compound concentrations decreased from approximately 43 mg/L in untreated OSPW to 10 mg/L following a 16-d retention time in the hybrid CWTS. Mean As and Zn concentrations decreased from 0.026 mg/L and 0.129 mg/L in untreated OSPW to 0.011–0.014 mg/L and 0.052–0.062 mg/L in wetland outflows, respectively. Cu and Pb mass decreased by 13–26% in the CWTS; however, evaporative concentration masked removal (in terms of total metal concentrations). Toxicity (in terms of C. dubia survival and reproduction) of OSPW was eliminated following treatment. Results demonstrate that hybrid CWTSs can effectively degrade NAs and alleviate toxicity associated with metals and organics in OSPW.

Floating Wetland Treatment of Acid Mine Drainage using Eichhornia crassipes (Water Hyacinth).

Background.Acid mine drainage (AMD) is a major environmental impact associated with the mining industry. Elevated acidic conditions resulting from the discharge of AMD into the surrounding environment can cause heavy metals to dissolve and transport through water streams and accumulate in the aquatic environment, posing a risk to the health of living organisms. There have been several novel approaches in the remediation of AMD involving passive treatment techniques. The constructed treatment wetland approach is a passive remediation option that has proven to be a cost effective and long-lasting solution in abating toxic pollutant concentrations.Objectives.The present study investigates the applicability of water hyacinth (Eichhornia crassipes), a tropical aquatic plant with reported heavy metal hyper-accumulation in microcosm floating wetland treatment systems designed to remediate AMD with copper (Cu) and cadmium (Cd) concentrations exceeding threshold limits.Methods.Twelve water hyacinth samples were prepared with varying concentrations of Cu (1 mg/L, 2 mg/L, 4 mg/L) and Cd (0.005 mg/L, 0.01 mg/L, 0.02 mg/L). Water samples of 5 ml each were collected from each sample at 24-hour intervals for analysis with an atomic absorption spectrometer.Results.Plant growth varied according to Cu and Cd concentrations and no plants survived for more than 14 days. There was a significant discrepancy in the rate at which the Cd concentrations abated. The rate of reduction was rapid for higher concentrations and after 24 hours a substantial reduction was achieved. There was a reduction in Cu concentration after the first 24-hour period, and after the next 24-hour period the concentrations were again elevated in the samples at initial concentrations of 2 mg/L and A4 mg/L. 4 mg/L Cu concentration was shown to be toxic to the plants, as they had low accumulations and rapid dying was evident.Conclusions.Water hyacinth has the capability to reduce both Cu and Cd concentrations, except at an initial concentration of 4 mg/L of Cu, which was toxic to the plants.Competing Interests.The authors declare no competing financial interests.

Clean WateR3: evaluation of three treatment technologies to remove contaminants from recycled production runoff

Increased competition for freshwater resources, negative environmental impacts associated with non-treated agricultural and specialty crop production runoff, and potential for more restrictive regulations concerning water use and disposal have provided growers with significant incentives to develop onsite water treatment to enable water reuse. As part of the Clean WateR3 project initiatives, three ecologically based treatment technologies are being evaluated for potential to remove contaminants (e.g., phytopathogens, pesticides, or mineral nutrients) from recycled irrigation runoff. An experimental floating treatment wetland system was assembled to assess the efficacy of nutrient uptake by two types of plants (Juncus effusus L. and Pontederia cordata L.) in two different levels of fertilizer concentration (5 or 12 ppm nitrogen). Initial findings suggest that Pontederia cordata is more efficient at nutrient (phosphorus and nitrogen) uptake than Juncus effusus. In order to determine the potential of vegetated channels to remediate phytopathogens, namely Phytophthora, from irrigation runoff, a series of greenhouse trials were conducted to test the susceptibility of seven wetland plant species to infection by five species of Phytophthora commonly found at plant nurseries in the southeastern United States. Preliminary data suggest that these seven plant species do not appear to be susceptible to the five species of Phytophthora tested. Subsurface bioreactors containing woodchips and haydite have been constructed onsite at an experimental nursery in central Michigan. Experiments investigating the effects of the pesticide chlorpyrifos on denitrifying microbial communities will commence in early Spring 2017.

Macrophytes Potentials of Indigenous Plant Species for Faecal Sludge Constructed Wetland Treatment System

Constructed Wetland technology has positive potentials for the management of faecal sludge in developing countries of Sub-Saharan Africa. However, identification of indigenous plant species that can survive the high levels of faecal sludge toxicity is a major challenge to its application. Preliminary study highlighted a high complexity of potential macrophytes species identification within the Sahelian context. This study is a preliminary stage of acclimatising four indigenous plant species Setaria verticillata (SV), Cymbopogon nardus (CN), Bambusa vulgaris (BV) and Typha latifolia L. (TL) to wastewater contamination in pot experiment. Macrophytes were subjected to wastewater irrigation from maturation basin of the 2iE Ouagadougou campus wastewater treatment plant. Macrophytes growth was monitored weekly by three growth parameters (No. of Plants per pot, Plant Height and No. of Leaves per pot). Initial plant height of 46.6, 75.7 and 61.7cm for SV, BV and TL, increased to 98, 103.1 and 93.5 cm after 13, 11 and 8 weeks of planting respectively. After 11 weeks of planting the average height of CN, reduced from 66.3 to 42 cm. Number of plants averagely increased from 25 to 130, 4 to15, 4 to 10 and 4 to 8 respectively for SV, CN, BV and TL. Average leaves per pot increased from 95 to 839, 19 to 67, 368 to 508 and 4 to 49 for SV, CN, BV and TL respectively. Variations of average growth rate among species were statistically insignificant. The results thus indicate satisfactory reed potentials with wastewater acclimatisation.

Performance of a large-scale wetland treatment system in treating tailwater from a sewage treatment plant

Water quality standards pertaining to effluent from sewage treatment plants (STPs) in China have become more stringent, requiring upgrading of STPs and entailing huge capital expenditure. Wetland treatment systems (WTSs) are a low-cost and highly efficient approach for deep purification of tailwater from STPs. The Hongze WTS (HZ-WTS), a large-scale surface-flow constructed wetland, with a total area of 55.58ha and a treatment capacity of 4×104m3day–1, was built for the disposal of tailwater from STPs. The aim of the present study was to evaluate the performance of HZ-WTP with regard to seasonal variations and to compare treatment costs with those of other STPs. The performance of the HZ-WTS was evaluated in 2013 using online monitoring. HZ-WTS exhibited significant removal efficiency of ammonia nitrogen (NH4+-N), chemical oxygen demand and total phosphorus (mean±s.d., percentage removal efficiency 56.33±70.44, 55.64±18.58 and 88.44±22.71% respectively), whereas there was significant seasonal variation in the efficiency of NH4+-N removal. In addition, the average treatment cost was ¥0.17m–3, significantly lower than the corresponding value for other STPs. Therefore, WTSs are recommended for use with STPs in order to improve waste water quality in a cost-effective manner.

Constructed Wetlands and their Role in Remediation of Industrial Effluents via Plant-Microbe Interaction – A Mini Review

Constructed Wetlands and their Role in Remediation of Industrial Effluents via Plant-Microbe Interaction – A Mini Review

A preliminary study to design a floating treatment wetland for remediating acid mine drainage-impacted water using vetiver grass (Chrysopogon zizanioides).

Acid mine drainage (AMD) is extremely acidic, sulfate-rich effluent from abandoned or active mine sites that also contain elevated levels of heavy metals. Untreated AMD can contaminate surface and groundwater and pose severe ecological risk. Both active and passive methods have been developed for AMD treatment consisting of abiotic and biological techniques. Abiotic techniques are expensive and can create large amounts of secondary wastes. Passive biological treatment mainly consists of aerobic or anaerobic constructed wetlands. While aerobic wetlands are economical, they are not effective if the pH of the AMD is <5. Anaerobic wetlands use organic-rich substrates to provide carbon source to iron- and sulfate-reducing bacteria. The efficiency of these systems declines overtime and requires continuous maintenance. Our objective is to develop an alternative, low-cost, and sustainable floating wetland treatment (FWT) system for AMD for the abandoned Tab-Simco coal mining site in Illinois using vetiver grass (Chrysopogon zizanioides). Tab-Simco AMD is highly acidic, with mean pH value of 2.64, and contains high levels of sulfate and metals. A greenhouse study was performed for a 30-day period in order to screen and optimize the necessary parameters to design a FWT system. Water quality and plant growth parameters were continuously monitored. Results show significant SO42- removal, resulting in increased pH, particularly at higher planting densities. Vetiver also helped in metal removal; high amounts of Fe, Zn, and Cu were removed, with relatively lower amounts of Pb, Al, and Ni. Iron plaque formation on the root was observed, which increased metal stabilization in root and lowered root to shoot metal translocation. Vetiver was tolerant of AMD, showing minimal change in biomass and plant growth. Results obtained are encouraging, and a large scale mesocosm study is now in progress, as the next step to develop the vetiver-based system for AMD treatment.

The use of constructed wetlands for the treatment of industrial wastewater

Abstract Constructed wetlands are characterized by specific conditions enabling simultaneous various physical and biochemical processes. This is the result of specific environment for the growth of microorganisms and hydrophytes (aquatic and semiaquatic plants) which are capable of living in aerobic, anaerobic and facultative anaerobic conditions. Their interaction contributes to the intensification of oxidation and reduction responsible for the removal and retention of pollutants. These processes are supported by sorption, sedimentation and assimilation. Thanks to these advantages, treatment wetland systems have been used in communal management for over 50 years. In recent years, thanks to its advantages, low operational costs and high removal efficiency, there is growing interest in the use of constructed wetlands for the treatment or pre-treatment of various types of industrial wastewater. The study analyzes current use of these facilities for the treatment of industrial wastewater in the world. The conditions of use and efficiency of pollutants removal from readily and slowly biodegradable wastewater, with special emphasis on specific and characteristic pollutants of particular industries were presented. The use of subsurface horizontal flow beds for the treatment of industrial wastewater, among others from crude oil processing, paper production, food industry including wineries and distillery, olive oil production and coffee processing was described. In Poland constructed wetlands are used for the treatment of sewage and sludge from milk processing in pilot scale or for dewatering of sewage sludge produced in municipal wastewater treatment plant treating domestic sewage with approximately 40% share of wastewater from dairy and fish industry. In all cases, constructed wetlands provided an appropriate level of treatment and in addition the so-called ecosystem service.

Perfluoroalkyl and polyfluoroalkyl substances removal in a full-scale tropical constructed wetland system treating landfill leachate

Landfill leachate is often an important source of emerging organic contaminants including perfluoroalkyl and polyfluoroalkyl substances (PFASs) requiring proper treatment to protect surface water and groundwater resources. This study investigated the occurrence of PFASs in the leachate of a capped landfill site in Singapore and the efficacy of PFASs removal during flow through a constructed wetland (CW) treatment system. The CW treatment system consists of equalization tank, aeration lagoons, sedimentation tank, reed beds and polishing ponds. Target compounds included 11 perfluoroalkyl acids (PFAAs) (7 perfluoroalkyl carboxylic acids (PFCAs) and 4 perfluoroalkane sulfonates (PFSAs)) and 7 PFAA precursors. Although total PFASs concentrations in the leachate varied widely (1269 to 7661 ng/L) over the one-year sampling period, the PFASs composition remained relatively stable with PFCAs consistently being predominant (64.0 ± 3.8%). Perfluorobutane sulfonate (PFBS) concentrations were highly correlated with total PFASs concentrations and could be an indicator for the release of PFASs from this landfill. The release of short-chain PFAAs strongly depended on precipitation whereas concentrations of the other PFASs appeared to be controlled by partitioning. Overall, the CW treatment system removed 61% of total PFASs and 50–96% of individual PFASs. PFAAs were removed most efficiently in the reed bed (42–49%), likely due to the combination of sorption to soils and sediments and plant uptake, whereas most of the PFAA precursors (i.e. 5:3 fluorotelomer carboxylate (5:3 acid), N-substituted perfluorooctane sulfonamides (N-MeFOSAA and N-EtFOSAA)) were removed in the aeration lagoon (>55%) by biodegradation. The sedimentation tank and polishing ponds were relatively inefficient, with only 7% PFASs removal.

Artificial floating islands for water quality improvement

Artificial floating islands (AFIs) are a variation of wetland treatment systems for water quality improvement. This paper provides a review concerning AFIs in terms of their development, classification, and applications in the removal of nutrients, heavy metals, and chemical oxygen demand on waterways. The role of microorganisms, aquatic plants, and aquatic animals in AFIs for water decontamination and purification was also discussed. Additionally, some key factors influencing the AFIs’ performances were discussed and comparisons between AFIs and constructed wetlands were reviewed. Finally, further perspectives of artificial floating islands were identified to possibly improve their performances. The understanding of the mechanisms in AFIs that drive removal of various contaminants to improve water quality is crucial, and is also highlighted in this paper.

Evaluation of algal bloom mitigation and nutrient removal in floating constructed wetlands with different macrophyte species

Algal blooms resulting from the eutrophication of surface waters represent a significant ecological and water treatment issue. The potential for wetland systems to act as sinks for various types of pollutants indicates their potential for mitigating algal blooms. Although nutrient uptake in terrestrial treatment wetland systems has received substantial attention in the literature, relatively little is known about the mechanisms involved in floating constructed wetland (FCW) function for algal control and whether plant species can optimise performance. Here, the effect of FCWs on water quality including nutrient levels and algal biomass was investigated, along with the effect of planting with different species of macrophyte. All the planted FCWs showed significant potential for algal bloom mitigation in both hypereutrophic and mesotrophic systems; algal biomass control is proposed to be due to the direct uptake of nitrate and phosphate via macrophyte roots, rather than algaecidal effect of phenolic compounds. Dissolved organic carbon (DOC) release was found to differ between species, with implications for drinking water treatment.

The uptake of mixed PAHs and PBDEs in wastewater by mangrove plants under different tidal flushing regimes

Wastewater often contains mixed toxic pollutants, and the contribution of plant uptake in constructed wetland treatment systems is affected by environmental conditions, particularly tidal flushing. In this study, the uptake of wastewater-borne pollutants, including a mixture of polycyclic aromatic hydrocarbons (PAHs) and polybrominated diphenyl ethers (PBDEs) congeners, by two mangrove plant species, namely Excoecaria agallocha L. and Kandelia obovata Sheue, Liu & Yong, under different tidal flushing regimes was investigated. Results showed that Fe plaque formed on root surfaces could immobilize wastewater-borne PAHs and PBDEs. At the end of 8-month wastewater treatment, most of the pollutants removed by plants ended up in Fe plaque, with 0.12–20.83% of total PAHs and 0.78–24.76% of total PBDEs added to the microcosm retained in Fe plaque. On the contrary, the percentages of PAHs and PBDEs taken up by plant tissues were relatively small, ranging from not detected to 0.09% and from 0.01 to 2.00%, respectively. More uptake of Fe plaque-immobilized PAHs and PBDEs was found in K. obovata than in E. agallocha, leading to more plant damages in the former species due to its weaker root outer layers. While E. agallocha with stronger root protective outer layer was able to uptake more PAHs and PBDEs from wastewater but immobilize in Fe plaque than that of K. obovata. In both plant species, tidal flushing regimes significantly affected the immobilization of PAHs and PBDEs in Fe plaque, and more frequent tidal flushing led to higher percentages of immobilization. This is the first study demonstrating that E. agallocha was a more suitable mangrove plant species to remove wastewater-borne PAHs and PBDEs than K. obovata, and the significance of tidal flushing on performance of constructed mangrove wetlands.

Design of real-time and long-term hydrologic and water quality wetland monitoring stations in South Florida, USA

Hydrologic regimes in tropical and subtropical regions (e.g. hurricanes, tropical storms, and droughts) impact biogeochemical processes in created and restored wetlands with variability of wet/dry seasons and extreme weather events. Our South Florida Wetland Monitoring Network (SFWMN) with three real-time hydrologic, water quality, and meteorological field stations was established by the Everglades Wetland Research Park of Florida Gulf Coast University in the subtropical Southwest Florida, USA, beginning in 2012. The stations include a restored freshwater marsh (RFM) and adjacent meteorological field station; a restored brackish water marsh (RBM); and a created freshwater treatment wetland system and adjacent meterological station (CFTW). Continuous observations of water depth, temperature, salinity, and pH for the period of January 2012 to January 2016 indicate significant differences among the restored freshwater marsh, the restored brackish marsh, and the created freshwater treatment wetlands for water temperature and pH for wet and dry seasons. The brackish wetland salinity fluctuated between 26.16 (in the dry season) to 1.03ppt (in the wet season).The real-time dataset allowed up-to-date information of the frequency and duration of severe weather events illustrating, for example, that 70% of the 2012 annual rainfall (1129mm) occurring in July and August with a 75.4mm precipitation during one event—tropical storm Isaac on August 26–28, 2012. This storm led to a water stage peak in the brackish wetland due to excessive watershed runoff, not tidal surges, and salinity decreased from 22.3 to 5.5ppt.The coefficient of variation (CV) for water depth and water quality from all wetland monitoring stations exhibited similar variations during all seasons, except when the salinity for the brackish marsh (RBM) had the highest CV values (1.02) in the wet season. Principal component analysis (PCA) at each station identified the variance in water depth and water quality parameters as due to seasonal changes of precipitation in distinct wet and dry seasons. The data from these monitoring stations are also used for research by scholars and students as well as for teaching a better understanding of wetlands dynamics and function in the classroom. As a whole, these stations are being used to bring awareness about the fragile and unique hydrological conditions of wetlands in subtropical Southwest Florida, especially for long-term conditions related to sea level changes and more frequent tropical storms.

Tracking the fate of nitrate through pulse-flow wetlands: A mesocosm scale 15N enrichment tracer study

Quantitative information about the fate of applied nitrate (NO3-N) in pulse-flow constructed wetlands is essential for designing wetland treatment systems and assessing their nitrogen removal services for agricultural and stormwater applications. Although many studies have documented NO3-N losses in wetlands, controlled experiments indicating the relative importance of different processes and N sinks are scarce. In the current study, 15NO3-N isotope enrichment tracer experiments were conducted in wetland mesocosms of two different wetland soil types at two realistic agricultural NO3-N source loads. The 15N label was traced from the source NO3-N into plant biomass, soil (including organic matter and ammonium), and N-gas constituents over 7–10day study periods. All sinks responded positively to higher NO3-N loading. Plant uptake exceeded denitrification 2–3 fold in the low NO3-N loading experiments, while both fates were nearly equivalent in the high loading experiments. One to two years later, soils largely retained the assimilated tracer N, whereas plants had lost much of it. Results demonstrated that plant and microbial assimilation in the soil (temporary N sinks) can exceed denitrification (permanentN loss) in pulse-flow environments and must be considered by wetland designers and managers for optimizing nitrogen removal potential.

Study on the efficiency of continuous flow-based constructed wetland system for grey water treatment

Water is inevitable for our life. Due to the population growth, there is a tremendous pressure on the existing fresh water resources such as surface water and ground water. Increasing water demand and improper usage of potable water lead to scarcity of fresh water resources. Globally, treating grey water is a real constraint to minimize the problem of water scarcity. The continuous flow-based constructed wetland system for grey water treatment is a technique for reusing the domestic grey water and it is a low-cost method. The current study was aimed to evolve a suitable user-friendly treatment system for handling the household grey water. In the present study, grey water has been collected from the Bharathidasan University and it has been treated with biofiltration and rhizhodegradation techniques using continuous flow-based constructed wetland system. The system has been found as more effective for treating the Physico-chemical parameters such as suspended solids, pH, electrical conductivity, TS, TDS, DO, BOD, COD, TOC, CO3, HCO3, SO4, NO3, PO4, Ca, Mg, Na, K, total hardness, calcium hardness, chloride, and total alkalinity. The results reported the reduction in the biological oxygen demand (89%), chemical oxygen demand (81%), DO (95%), carbonate (100%), sodium (65%), and potassium (85%).It also examined the benefits and risks associated with the results in the reuse of domestic grey water for the purpose of vegetable gardening, irrigation, and toilet flushing. Consequently, this biofiltration method is natural, simple, and low cost-effective treatment in a holistic manner.

MANAGEMENT OF ACIDIC MINE WASTE WATER BY CONSTRUCTED WETLAND TREATMENT SYSTEMS: A BENCH SCALE STUDY

Constructed wetlands have emerged as a viable option for treatment of acidic mine wastewater. Bench scale experiments were conducted, to evaluate the performance of wetland treatment system, with emergent macrophyte Desmostachya bipinnata and substrate (containing powdered goat manure, wood shavings and soil) for 24, 48, 72, 96 and 168 hours of retention period for different water column heights (100mm, 150mm and 200mm). Within 24 hours of retention period the pH increased from 2.93 to 7.22, alkalinity increased from zero mg/L to 204.30 mg/L as CaCO 3 , electric conductivity decreased by 27.94 to 35.93 percent, turbidity decreased by 30.14 to 66.65 percent, sulphate reduced by 21.52 to 28.09 percent, acidity reduced by 88.89 to 100 percent, hardness reduction was 18.18 to 26.07 percent. Potential metal removal rates was 95.20 to 95.51 percent for Fe, 88.77 to 91.72 percent for Cu, 76.75 to 78.21 percent Zn, 88.80 to 90.12 Pb, 67.65 to72.33 percent Co, 29.60 to 63.76 percent Ni and 35.90 to 76.44 percent Mn respectively. Keywords: Acidic Mine Water,Treatment, Constructed Wetland, D. bipinnata

Metal and metalloid sequestration in a constructed wetland system for treatment of landfill leachate during 2003-2012

The treatment of landfill leachate in constructed wetland systems is a common practice in Europe. However, very few studies were made to evaluate their performance over a long period of time. A free surface constructed wetland system consisting of sediment traps followed by 10 ponds connected with overflows was built at Atleverket near Örebro, Sweden in 2001. It receives pre-treated leachate from the municipal landfill. As part of the wetland monitoring programme a large data set on the surface concentrations of 15 metals and 2 metalloids has been collected from different sampling sites within the wetland during the operation period. In this study, the data from inlet and outlet of the wetland were compiled and analysed. The aim of this paper is therefore to estimate the removal efficiency of metals and metalloids using data on concentrations and flow and investigate the effect of wetland age on removal pattern. The elements with the highest removal efficiency were Al, As, Ba, Ca, Cr, Cu, Fe, Mn, Pb, V and Zn ranging from 95% for Pb to 65 % for Ca. The elements with the lowest reduction were B, Co K, Mg, Ni and S ranging from Co 56 % to 40 % for S. It was found that the removal efficiency was not related to inlet concentrations of the elements as the elements with high and low inlet concentrations were found in both groups. Analysis of reduction pattern also revealed that the group with higher removal efficiency showed fairly constant outlet concentrations during the study period, while the elements with lower removal efficiency demonstrated variable outlet concentrations. No statistical difference in removal due to age of the wetland was found. The study results showed that the wetland system has high removal efficiency of metals and metalloids and the removal pattern is not affected by age of the wetland. The influence on reduction due to leachate characteristics, wetland design and retention time will be discussed.

USING FLOATING WETLAND TREATMENT SYSTEMS TO REDUCE STORMWATER POLLUTION FROM URBAN DEVELOPMENTS

Floating treatment wetland (FTW) systems are an innovative stormwater treatment technologycurrently being trialled in Australia. FTWs provide support for selected plant species to remove pollutants fromstormwater discharged into a storage basin. The plant roots provide large surface areas for biofilm growth,which serves to trap suspended particles and enable the biological uptake of nutrients. FTWs can be installedat the start of the construction phase and can therefore start treating construction runoff almost immediately.FTWs have the potential to provide a full range of stormwater runoff treatment (e.g. sediment and nutrientremoval) from the construction phase onwards. A 101 m2 FTWs has been installed within a greenfielddevelopment site on the Sunshine Coast, in Australia. The two-year research study investigated the pollutionremoval performance of the FTW for two different locations, one with low and one with moderate influentpollutant concentrations. This paper presents the research methodology used, and the initial study results ofthe treatment efficiency of FTWs.