Nitrate removal from groundwater using constructed wetlands under various hydraulic loading rates

This study set up two flow-through pilot-scale constructed wetlands with the same size but various flow patterns (free water surface flow (FWS) and subsurface flow (SSF)) to receive a nitrate-contaminated groundwater. The effects of hydraulic loading rate (HLR) on nitrate removal as well as the difference in performance between the various types of wetlands were investigated. Nitrate removal rates of both wetlands increased with increasing HLR until a maximum value was reached. The maximum removal rates, occurred at HLR of 0.12 and 0.07 m d(-1), were 0.910 and 1.161 g N m(-2)d(-1) for the FWS and SSF wetland, respectively. After the maximum values were reached, further increasing HLR led to a considerable decrease in nitrate removal rate. Nitrate removal efficiencies remained high (>85%) and effluent nitrate concentrations always satisfied drinking water standard (<10mg NO3-NL(-1)) when HLR did not exceed 0.04 m d(-1) for both FWS and SSF wetlands. The first-order nitrate removal rate constant tends to decrease with increasing HLRs. The FWS wetland provided significantly higher (p<0.05) organic carbon in effluent than the SSF wetland, while the SSF wetland exhibited significantly (p<0.05) lower effluent DO than the FWS wetland. However, there was no significant difference (p>0.05) in nitrate removal performance between the two types of constructed wetlands in this study except in one trial operating at HLR of 0.06-0.07 m d(-1).     

Removal of polycyclic aromatic hydrocarbons and linear alkylbenzene sulfonates from domestic wastewater in pilot constructed wetlands and a gravel filter

Removal efficiencies of polycyclic aromatic compounds (PAHs) and linear alkyl benzene sulfonates (LAS) were evaluated in a pilot-scale constructed wetland (CW) system combining a free water surface wetland, a subsurface wetland and a gravel filter in parallel. The effect of parameters such as temperature and mass loading rate was also examined. The subsurface constructed wetland system was found to have the overall best performance on pollutants removal. In particular, the average removal of PAHs and LAS was 79.2% and 55.5% for the SSF (Subsurface Flow) constructed wetland, 68.2% and 30.0% for the FWS (Free Water Surface) constructed wetland and 73.3% and 40.9% for the gravel filter, respectively. Removal efficiency and the estimated first-order volumetric removal rate constant (k_v) for both PAHs and LAS decreased with increasing water temperature. The experimental results suggest that the absorption in solid media is the main mechanism for xenobiotics removal in constructed wetlands and that the overall performance of the SSF wetland is significantly better than the FWS wetland or the gravel filter.     

Occurrence and removal of parasites, enteric bacteria and faecal contamination indicators in wastewater natural reclamation systems in Tenerife-Canary Islands, Spain

Two wastewater natural reclamation systems (WWNRS) have been compared regarding their efficiencies on faecal bacteria removal and the persistence of enteric pathogens. These WWNRS are constituted of a combination of anaerobic treatment, small sub-surface flow constructed wetland refilled of volcanic ashes and a final pond as water reservoir. Faecal coliforms, enterococci, Escherichia coli, Clostridium perfringens, somatic coliphages, Salmonella sp., Campylobacter sp., Cryptosporidium sp., Giardia sp. and helminth eggs were analyzed in constructed wetlands inlet and outlet and storage pond effluent. Low numbers of protozoan positive samples (4.54% in Albergue de Bolico for both protozoa, and 19.05% in Carrizal Alto for Giardia sp.) and absence of helminth eggs were found. Both systems demonstrated efficient reduction of faecal contamination indicators in the wastewaters (removal rates values of 2 log₁₀). The natural systems for wastewater treatment used to be efficient in Salmonella abatement, this fact was confirmed in the reported systems, since enterobacteriaceae were found in only one of the effluents. Campylobacter species associated with the access of animals to storage ponds were detected in the reclaimed water.     

Giardia and Cryptosporidium removal from waste-water by a duckweed (Lemna gibba L.) covered pond

AIMS: To determine the ability of duckweed ponds used to treat domestic waste-water to remove Giardia and Cryptosporidium. METHODS AND RESULTS: The influent and effluent of a pond covered with duckweed with a 6 day retention time was tested for Giardia cysts, Cryptosporidium oocysts, faecal coliforms and coliphage. Giardia cysts and Cryptosporidium oocysts were reduced by 98 and 89%, respectively, total coliforms by 61%, faecal coliforms by 62% and coliphage by 40%. There was a significant correlation between the removal of Giardia cysts and Cryptospordium oocysts by the pond (P < 0.001). Influent turbidity and parasite removal were also significantly correlated (Cryptosporidium and turbidity, P=0.05; Giardia and turbidity, P=0.01). CONCLUSIONS: The larger organisms (parasites) probably settled to the bottom of the pond, while removal of smaller bacteria and coliphages in the pond was not as effective. SIGNIFICANCE AND IMPACT OF THE STUDY: Duckweed ponds may play an important role in wetland systems for reduction of Giardia and Cryptosporidium.     

Effectiveness of Various Small‐Scale Constructed Wetland Designs for the Removal of Iron and Zinc from Acid Mine Drainage under Field Conditions

A system of planted and unplanted small‐scale subsurface flow (SSF) and surface flow (SF) constructed wetlands together with hydroponic systems (HP) were installed to compare the removal efficiencies of Fe and Zn from acid mine drainage (AMD) under long‐term field conditions. Maximum removal of 94–97 % (116–142 mg/m² d) for Fe and 69–77 % (6.2–7.9 mg/m² d) for Zn was calculated for the planted soil systems. The planted SSF was most sensitive to heavy rain fall. Short‐term increases of the metal concentration in the outflows, short‐term breakdowns of the Fe removal and continual long‐term breakdowns of the Zn removal were observed. In contrast to Zn removal, all wetland types are applicable for Fe removal with maximum removal in the range of 60–98 %. Most of the removed Fe and Zn was transformed and deposited inside the soil bed. The amount absorbed by the plants (0.03 to 0.3 %) and gravel‐associated soil beds (0.03 to 1.7 %) of the total input were low for both metals. The response of the planted SSF to rainfall suggests a remobilization of metals accumulated inside the rhizosphere and the importance of buffering effects of the surface water layers of SF systems. The importance of plants for metal removal was shown.     

Characterization of Microbial Communities and Composition in Constructed Dairy Wetland Wastewater Effluent

Constructed wetlands have been recognized as a removal treatment option for high concentrations of contaminants in agricultural waste before land application. The goal of this study was to characterize microbial composition in two constructed wetlands designed to remove contaminants from dairy washwater. Water samples were collected weekly for 11 months from two wetlands to determine the efficiency of the treatment system in removal of chemical contaminants and total and fecal coliforms. The reduction by the treatment was greatest for biological oxygen demand, suspended solids, chemical oxygen demand, nitrate, and coliforms. There was only moderate removal of total nitrogen and phosphorus. Changes in the total bacterial community and ammonia-oxidizing bacterial composition were examined by using denaturing gradient gel electrophoresis (DGGE) and sequencing of PCR-amplified fragments of the gene carrying the α subunit of the ammonia monooxygenase gene (amoA) recovered from soil samples and DGGE bands. DGGE analysis of wetlands and manure samples revealed that the total bacterial community composition was dominated by bacteria from phylogenetic clusters related to Bacillus, Clostridium, Mycoplasma, Eubacterium, and Proteobacteria originally retrieved from the gastrointestinal tracts of mammals. The population of ammonia-oxidizing bacteria showed a higher percentage of Nitrosospira-like sequences from the wetland samples, while a higher percentage of Nitrosomonas-like sequences from manure, feces, raw washwater, and facultative pond was found. These results show that the wetland system is a natural process dependent upon the development of healthy microbial communities for optimal wastewater treatment.     

Mechanisms for Parasites Removal in a Waste Stabilisation Pond

A waste stabilisation pond (WSP) system formed by two anaerobic ponds, a facultative pond and a maturation pond was studied from December 2003 to September 2004 in north-western Spain in order to evaluate its efficiency in the removal of faecal indicator bacteria (total coliforms, Escherichia coli, faecal streptococci), coliphages, helminth eggs and protozoan (oo)cysts (Cryptosporidium and Giardia). Furthermore, sediment samples were collected from the bottom of the ponds to assess the settling rates and thus determine the main pathogen removal mechanisms in the WSPs system. The overall removal ranged from 1.4 log units for coliphages in the cold period to 5.0 log units for E. coli in the hot period. Cryptosporidium oocysts were reduced by an average of 96%, Giardia cysts by 98% and helminth eggs by 100%. The anaerobic ponds showed significantly higher surface removal rates (4.6, 5.2 and 3.7 log (oo)cysts/eggs removed m⁻² day⁻¹, respectively) than facultative and maturation ponds. Sunlight and water physicochemical conditions were the main factors influencing C. parvum oocysts removal both in the anaerobic and maturation ponds, whereas other factors like predation or natural mortality were more important in the facultative pond. Sedimentation, the most commonly proposed mechanism for cyst removal had, therefore, a negligible influence in the studied ponds.     

Comparison of free water and horizontal subsurface treatment wetlands

The two most prevalent types of treatment wetland, especially during the early history of the technology, are free water surface (FWS) and horizontal subsurface flow (HSSF) wetlands. The several factors involved in the choice of which alternative to choose include size, cost, operability, together with health and nuisance issues and ancillary benefits. Contaminant removal performance differs by constituent, with the advantage to FWS for moderate to high biochemical oxygen demand (BOD), TSS, ammonia, total nitrogen and phosphorus. HSSF are more effective for tertiary BOD levels, nitrate and pathogens. Superpositions of the loading data show that the respective data clouds overlap virtually entirely for HSSF and FWS wetlands. There is little or no performance difference when they are compared on this areal basis. In general, there is little or no advantage of HSSF for space saving. In cold climates, HSSF systems are less cold sensitive, and easier to insulate for winter operation. The use of winter storage enables FWS to be used in freezing conditions, but the cost makes that option comparable to the more expensive HSSF. In general, economics do not favor the choice of HSSF wetlands. Factors other than reduction performance are also important in the selection process. Other principal reasons for selecting the HSSF option over the FWS option are prevention of human health contact problems, mosquito control and minimization of wildlife interactions.     

Pathogen removal in high-rate algae pond: state of the art and opportunities

High-rate algae ponds (HRAPs) are wastewater treatment systems that enable combining cost-efficient secondary treatment at small scale with the production of a harvestable biomass for subsequent valorisation (e.g. biofuel). However, there is still limited data on pathogen removal during long-term HRAP operation with real effluents. This critical review evaluates the potential significance of mechanisms driving pathogen removal in classical wastewater ponds in light of the specific environmental conditions occurring in HRAPs. We thus establish that the presence of algae (at high cell density) increases sunlight attenuation in HRAP and this attenuation negatively impacts sunlight-mediated pathogen removal. However, mixing may counteract the negative effect of light attenuation by increasing the frequency of pathogen exposure to high light intensity near the culture surface in HRAPs. The magnitude of sunlight-mediated pathogen removal is also likely increased at high pH and dissolved oxygen concentrations, two conditions frequently co-occurring in HRAPs harbouring intense algal activity. Exposure to high pH and toxic algae metabolites may further enhance pathogen decay in HRAPs but these mechanisms are still poorly understood. Finally, predation may be significant, but little is known about the quantitative impact of this mechanism in classical ponds and HRAPs. Overall, and with the exception of settling, all pathogen removal mechanisms known to occur in maturation ponds should remain significant in HRAPs. While this pathogen removal ability has been verified in a few studies, further research must now seek to develop a better mechanistic understanding based on the study of real systems.

     

Effects of vegetation on flow through free water surface wetlands

The one-dimensional Saint-Venant equations are modified to account for stem drag and volumetric displacement effects of dense emergent plants on free surface flow. The modified equations are solved with an implicit finite difference method to give velocities and depths for shallow flows through a vegetated wetland channel. Estimated flow profiles are used to investigate how vegetation density, downstream boundaries and aspect ratio affect detention time, an important parameter in determining nutrient and pollutant removal efficiencies of wetlands constructed to treat wastewater. Results show that free water surface wetlands may exhibit static, neutral or dynamic behavior. Under static conditions, the wetland behaves like a pond in which displacement effects caused by submerged plant mass invariably decrease detention times. Under dynamic conditions, stem drag induced by aquatic plants predominates and wetland detention times increase with vegetation density. These opposing responses are separated by a narrow neutral condition where the presence of vegetation has virtually no net effect on detention time. For a given flow rate and surface area, detention times and hence treatment efficiencies in vegetated free water surface wetlands can be managed to some degree by adjusting the downstream control or by changing the aspect ratio.     

Effectiveness of Differently Designed Small‐Scale Constructed Wetlands to Decrease the Acidity of Acid Mine Drainage under Field Conditions

Constructed wetlands are a near‐natural method for the treatment of acid mine drainages (AMD). Because of the different site‐specific wastewater qualities and the variability of the used constructed wetlands regarding design, it is difficult to compare their efficiencies on the basis of literature data (often specific removal rates are missing). The AMD treatment efficiencies (pH, acidity) of differently designed planted and unplanted small‐scale constructed wetlands (subsurface flow – SSF, surface flow – SF, and hydroponic – HP systems with an area of 0.55 m² each) were compared under long‐term field conditions. The planted SF was found to be most effective, reaching mean acidity removal in the range of 80–90 %, and most resistant in view of external influences (i.e., heavy rain events). The planted SSF also showed high efficiency (50–90 %), but much more sensitivity to rain events. In both systems, the pH increased from 3.3 (mean of the inflows) to above 4.5 in the outflows. The efficiencies of the unplanted SF were insufficient and in the range of the (planted and unplanted) HP, i.e., smaller than 40 %. In general, the importance of plants for the success of the neutralization processes could be concluded.     

Characterization of microbial communities and composition in constructed dairy wetland wastewater effluent

Constructed wetlands have been recognized as a removal treatment option for high concentrations of contaminants in agricultural waste before land application. The goal of this study was to characterize microbial composition in two constructed wetlands designed to remove contaminants from dairy washwater. Water samples were collected weekly for 11 months from two wetlands to determine the efficiency of the treatment system in removal of chemical contaminants and total and fecal coliforms. The reduction by the treatment was greatest for biological oxygen demand, suspended solids, chemical oxygen demand, nitrate, and coliforms. There was only moderate removal of total nitrogen and phosphorus. Changes in the total bacterial community and ammonia-oxidizing bacterial composition were examined by using denaturing gradient gel electrophoresis (DGGE) and sequencing of PCR-amplified fragments of the gene carrying the alpha subunit of the ammonia monooxygenase gene (amoA) recovered from soil samples and DGGE bands. DGGE analysis of wetlands and manure samples revealed that the total bacterial community composition was dominated by bacteria from phylogenetic clusters related to Bacillus, Clostridium, Mycoplasma, Eubacterium, and Proteobacteria originally retrieved from the gastrointestinal tracts of mammals. The population of ammonia-oxidizing bacteria showed a higher percentage of Nitrosospira-like sequences from the wetland samples, while a higher percentage of Nitrosomonas-like sequences from manure, feces, raw washwater, and facultative pond was found. These results show that the wetland system is a natural process dependent upon the development of healthy microbial communities for optimal wastewater treatment.     

Evaluation of domestic wastewater treatment using microalgal-bacterial processes: effect of CO<Subscript>2</Subscript> addition on pathogen removal

Microalgal-bacterial processes represent a sustainable and cost-effective biotechnology able to promote efficient wastewater treatment, including natural pathogen removal (disinfection), as well as being able to perform CO₂ uptake and biogas upgrading. In this context, the influence of CO₂ supply from a synthetic gas mixture (30% v/v CO₂) on the removal of pathogens (Pseudomonas, enterococci, and Escherichia coli) and total coliforms during secondary domestic wastewater treatment by a microalgal-bacterial symbiosis in a 180-L high-rate algal pond (HRAP) was investigated. The supply of CO₂ in the HRAP positively influenced the Pseudomonas aeruginosa removal, with the removal efficiency increasing from 97.4% (1.6 log) to 99.6% (2.5 log) without and with CO₂ supply, respectively. Likewise, the total coliform removal efficiency rose from 88.7% (1.1 log) to 99.4% (2.8 log). On the other hand, the effect of CO₂ supply on enterococci (99.7% and 2.6 log) and Escherichia coli (98.6% and 2.2 log) removal was negligible.     

Water quality performance of treatment wetlands in the Imperial Valley,California

Two demonstration treatment wetland systems were studied for over four years. Both consisted of sedimentation basins, followed by wetland cells. The Imperial, CA system had four wetland cells totaling 4.7 ha, 25% vegetated with bulrushes (Schoenoplectus californicus), and the Brawley, CA system had two wetland cells totaling 1.8 ha, also 25% vegetated with bulrushes. Imperial received irrigation runoff water at 30 cm/day, and Brawley received New River water at 11 cm/day, both with moderately high levels of nutrients, sediments and pathogens. The systems seeped 40–60% of the incoming water. The hydraulic efficiencies of the systems were high because of compartmentalization and high aspect ratios. Concentration reductions of TN, TP and TSS were 50%, 39%, and 97% at Imperial, and 73%, 50% and 96% at Brawley. Imperial achieved about 1.5 log₁₀ reductions in total coliforms, fecal coliforms and Escherichia coli, while Brawley achieved about 2.7 log₁₀ reductions. The sedimentation basins settled most of the incoming TSS, as well as the algal solids that were generated in the basins. Algal uptake removed nutrients in the basins, which were supersaturated with oxygen. The wetlands were effective in denitrification, and trapped the remaining and generated TSS. Removal rate constants, corrected for infiltration, were at the high end of those reported for other wetlands.     

Occurrence of Pathogenic Free‐Living Amoebae and Bacterial Indicators in a Constructed Wetland Treating Domestic Wastewater from a Single Household

Constructed wetlands are effective wastewater treatment systems because of their ability to remove large amounts of organic matter and pathogens. The goals of this study were to characterize the presence of pathogenic free‐living amoebae and bacterial indicators (total and fecal coliforms), and to ascertain the removal efficiencies of physical and chemical pollutants, in a constructed wetland treating domestic wastewater from a single household. Influent and effluent samples were collected monthly over a ten‐month period for biological, physical and chemical analyses. Thirty‐two species of free‐living amoebae were isolated from the system. The genus Acanthamoeba was the most frequently encountered (59 %) and was removed from the wastewater with the greatest efficiency (80 %). Removal of bacteria was low, the highest removal rates were found in August (4 logarithmic units) and January (3 logarithmic units). The average removal efficiencies of suspended solids, BOD₅ and ammoniacal nitrogen were 71.5 %, 50.6 % and 13.1 %, respectively. The relatively low removal efficiencies of the various bacteriological, physical and chemical parameters suggest that the hydraulic retention time was probably insufficient for optimal treatment to occur. The effluent quality was unacceptable for unrestricted irrigation of crops that are eaten uncooked.     

Side-by-side comparison of horizontal subsurface flow and free water surface flow constructed wetlands and artificial neural network (ANN) modelling approach

A horizontal subsurface flow (HSSF) and a free water surface flow (FWSF) constructed wetlands (4 m² of each) were set up on the campus of Harran University, Sanliurfa, Turkey. The main objective of the research was to compare the performance of two systems to decide the better one for future planning of wastewater treatment system on the campus. Both of the wetland systems were planted with Phragmites australis and Canna indica. During the observation period (10 months), environmental conditions such as pH, temperature and total chemical oxygen demand (COD), soluble COD, total biochemical oxygen demand (BOD), soluble BOD, total suspended solids (TSS), total phosphate (TP), total nitrogen (TN) removal efficiencies of the systems were determined. According to the results, average yearly removal efficiencies for the HSSF and the FWSF, respectively, were as follows: total COD (75.7% and 69.9%), soluble COD (85.4% and 84.3%), total BOD (79.6% and 87.6%), soluble BOD (87.7% and 95.3%), TN (33.2% and 39.4%), and TP (31.5% and 6.5%). Soluble COD and BOD removal efficiencies of both systems increased gradually since the start-up. After nine months of operation, above 90% removal of organic matters were observed. The treatment performances of the HSSF were better than that of the FWSF with regard to the removal of suspended solids and total COD at especially high temperatures. In FWSF systems, COD concentrations extremely exceeded the discharge limit values due to high concentrations of algae in spring months.The performance of the two systems was modelled using an artificial neural network-back-propagation algorithm. The ANN model was competent at providing reasonable match between the measured and the predicted concentrations of total COD (R = 0.90 for HSSF and R = 0.96 for FWSF), soluble COD (R = 0.90 for HSSF and R = 0.74 for FWSF) and total BOD (R = 0.94 for HSSF and R = 0.84 for FWSF) in the effluents of constructed wetlands.     

Nitrogen and phosphorus removal from wastewater by subsurface wetlands planted with Iris pseudacorus

Subsurface horizontal flow constructed wetlands are being evaluated for nitrogen (N) and phosphorus (P) removal from wastewater in this study through different gravel sizes, plant densities (Iris pseudacorus), effects of retention times (1 to 10 days) on N and P removal in continuously fed gravel wetland. The inlet and outlet samples were analyzed for TKN, NH₄-N, and NO₃-N, as standard methods. The planted wetland reactor with fine (SG) and coarse (BG) gravels removed 49.4% and 31.4% TKN, respectively, while unplanted reactors removed 43.4% and 26.8% TKN. Also, the efficiencies for NH₄-N were 36.7–43% and 21.6–25.4% for SG and BG planted reactors, respectively. The efficiencies for NO₃-N were 53.5–62.5% and 21.6–25.4% for SG and BG planted reactors, respectively. Roles of plants in SG reactors for O-PO₄ were 5–12% and 3–8% in BG. Also, the roles of plants in the reactors for TP were 9% and 7.4%. The minimum effective detention time for the removal of NO₃-N was 4–5 days. The subsurface constructed wetlands planted with I. pseudacorus can be an appropriate alternative in wastewater treatment natural system in small communities.     

Removal of Arsenic and Zinc Using Different Laboratory Model Wetland Systems

Industrial and mining activities are an increasing threat to natural sites like wetlands and ponds because of the pollution by heavy metals and particularly arsenic (As) which they create. Four different laboratory scale model wetland systems, simulating a subsurface water wetland (SWW), free water surface wetland (FWSW), hydroponic system (HP), and an algae pond (AP) were initially loaded with water containing 5 mg/L of Zn and 0.5 mg/L of As as the main contaminants. The experiments run discontinuously and water losses by evapotranspiration were compensated periodically by distilled water. SWW, FWSW and HP were planted with Juncus effusus. The aim of this investigation was above all to study the removal of As in anthropogenically influenced stagnant wetland systems. The AP system showed almost no changes in all parameters measured. In addition, for the HP system no depth gradients of the parameters could be observed. Nevertheless, the total concentrations decreased slightly over 90 days by about 25 % for As and about 30 % for Zn. Within the gravel bed systems (SWW and FWSW) As and Zn were completely removed from the water, whereas for both parameters the removal process in the SWW was considerably faster. In both gravel bed systems the changes in the iron concentrations and the redox potentials were completely different. During periods of comparatively low redox potential, the iron concentration of the pore water increased from 0.1 mg/L up to 3.0 mg/L for the FSW and to 6.8 mg/L for the SWW. In periods of a higher redox potential the iron concentration decreased. The utmost As removal from the water was found in the SWW. It was noted that this could not be explained by either the adsorption on the gravel or by the plant uptake alone. It can be assumed that by the combination of both effects within one system soil bound crystalline iron, which has a low As binding capacity, is dissolved and can function as a co‐precipitation agent for As in oxic zones such as possibly on the rhizoplane of helophytes.     

The fate of stormwater-associated bacteria in constructed wetland and water pollution control pond systems

The performances of a constructed wetland and a water pollution control pond were compared in terms of their abilities to reduce stormwater bacterial loads to recreational waters. Concentrations of thermotolerant coliforms, enterococci and heterotrophic bacteria were determined in inflow and outflow samples collected from each system over a 6-month period. Bacterial removal was significantly less effective in the water pollution control pond than in the constructed wetland. This was attributed to the inability of the pond system to retain the fine clay particles (< 2 microm) to which the bacteria were predominantly adsorbed. Sediment microcosm survival studies showed that the persistence of thermotolerant coliforms was greater in the pond sediments than in the wetland sediments, and that predation was a major factor influencing bacterial survival. The key to greater bacterial longevity in the pond sediments appeared to be the adsorption of bacteria to fine particles, which protected them from predators. These observations may significantly affect the choice of treatment system for effective stormwater management.     

Nitrogen mass balance and microbial analysis of constructed wetlands treating municipal landfill leachate

Experiments were conducted to investigate the feasibility of applying constructed wetlands to treat a sanitary landfill leachate containing high nitrogen and bacterial contents. Under a tropical condition (temperature of about 30 degrees C), the constructed wetland units operating at the hydraulic retention time of 8d yielded the best treatment efficiencies with BOD(5), TN and fecal coliforms removal of 91%, 96% and more than 99%, respectively. Cadmium removal in the SFCW bed was 99.7%. Mass balance analysis, based on total nitrogen contents of the plant biomass and dissolved oxygen and oxidation-reduction potential values, suggested that 88% of the input total nitrogen were uptaken by the plant biomass. Fluorescence in situ hybridization results revealed the predominance of bacteria, including heterotrophic and autotrophic, responsible for BOD(5) removal. Nitrifying bacteria was not present in the constructed wetland beds.