Long-term performance of constructed wetlands with horizontal sub-surface flow: Ten case studies from the Czech Republic

Constructed wetlands with horizontal sub-surface flow (HF CWs) have been in use in the Czech Republic since 1989. Evaluation of the long-term performance of horizontal sub-surface flow constructed wetlands in the Czech Republic indicates that removal of organics and suspended solids is very effective; efficiencies are steady throughout the year and are not affected by season and also by the length of operation. The results from systems treating wastewaters from combined sewer systems clearly indicate that HF CWs can very effectively cope with low inflow concentrations of organics and can provide effluent BOD₅ concentrations less than 5 mg l⁻¹. Phosphorus removal is seasonally steady but low as Czech constructed wetlands do not use special filtration media with high sorption capacity. This is not a problem, because in the Czech Republic, there is currently no discharge limit for phosphorus for wastewater treatment plants up to 2000 person equivalents (PE). Removal of ammonia-N is limited by lack of dissolved oxygen in filtration beds caused by permanent saturation. The removal of ammonia-N is steady over the life of operation but is affected by season but the decrease in ammonia removal efficiency during winter is not large.     

The potential for constructed wetlands for wastewater treatment and reuse in developing countries: a review

Constructed wetlands are among the recently proven efficient technologies for wastewater treatment. Compared to conventional treatment systems, constructed wetlands are low cost, are easily operated and maintained, and have a strong potential for application in developing countries, particularly by small rural communities. However, these systems have not found widespread use, due to lack of awareness, and local expertise in developing the technology on a local basis. This paper summarizes information on current methods used for wastewater treatment in developing countries, and briefly gives basic information on wetlands. The paper further examines the potential of constructed wetlands for wastewater treatment and reuse in developing countries by looking at the results of current research initiatives towards implementation of the technology in these countries. Future considerations in choosing constructed wetlands as wastewater treating systems in developing countries are highlighted.     

Growth of Phragmites australis and Phalaris arundinacea in constructed wetlands for wastewater treatment in the Czech Republic

Common reed (Phragmites australis) and reed canarygrass (Phalaris arundinacea) are two most commonly used plant species in constructed wetlands for wastewater treatment in the Czech Republic. Growth characteristics of both plants (biomass, stem count, and length) have been measured in 13 horizontal sub-surface flow constructed wetlands since 1992. The results revealed that while Phalaris usually reaches its maximum biomass as early as during the second growing season, Phragmites usually reaches its maximum only after three to four growing seasons. The maximum biomass of both species varies widely among systems and the highest measured values (5070 g m⁻² for Phragmites and 1900 g m⁻² for Phalaris) are similar to those found in eutrophic natural stands. The shoot count of Phragmites decreases after the second growing season while length and weight of individual shoots increases over time due to self-thinning process. Number of Phalaris shoots is the highest during the second season and then the shoot count remains about the same. Also the shoot length remains steady over years of constructed wetland operation.     

Subsurface horizontal-flow constructed wetlands for wastewater treatment: The Czech experience

The first full-scale constructed wetland (CW) in the Czech Republic was built in 1989 and there are now three tertiary systems and 50 secondary treatment facilities. We report here on the design and operational efficiencies of these facilities. All CWs have been designed with horizontal subsurface flow. Coarse sand, gravel and crushed stones with size fraction of 4–16 mm are commonly used as substrates. The area of vegetated beds ranges between 18 and 4500 m² and operational CWs are designed for population equivalent (PE) of 4 to 1,100. Common reed (Phragmites australis) is the most frequently used macrophyte species.Results from systems studied during 1994 and 1995 show that the effluent concentrations of organics and suspended solids (SS) are well below the required discharge limits. In most cases the final effluent BOD₅ concentration is <10 mg l^–1. The relationship between vegetated bed BOD₅ inflow loadings (L ₀) and outflow loadings (L) is very strong (r=0.92). Constructed wetlands with subsurface horizontal flow usually do not remove larger amounts of nitrogen and phosphorus. The results from five Czech constructed wetlands show that nitrogen removal varies among systems, but the amount of removed nitrogen is very predictable. A regression equation between nitrogen inflow loading (L ₀) and outflow loading (L) produces a strong correlation (r=0.98). The most important process responsible for phosphorus removal in wetlands is precipitation with soil Ca, Fe and Al. However, the subsurface horizontal flow constructed wetlands use mostly coarse gravel and/or sandy materials and this provides little or no P precipitation. Results from monitored systems in the Czech Republic show that the percentage phosphorus removal varies widely among systems and is lower than the percentage removal of organics and suspended solids.     

Performance of laboratory-scale constructed wetlands coupled with micro-electric field for heavy metal-contaminating wastewater treatment

This study reports the performance of laboratory-scale constructed wetlands coupled with micro-electric field (CWMEF) planted cannas (Canna generalis) for heavy metal-contaminating wastewater treatment. The CWMEF had a better performance for heavy metal (HM) removal from wastewater than did the ordinary constructed wetlands (CWs). Owing to the stimulation of the suitable voltage and electrical exposure time, cannas may grew better and in fact assimilated more metallic ions in CWMEF than in CWs. The environmental conditions in CWMEF, such as the higher pH by electrolysis of water, the presence of aluminum ions by anodizing of aluminum, caused chemical precipitation, physical adsorption and flocculation of metallic ions.     

Changes in the bacterial community structure in two-stage constructed wetlands with different plants for industrial wastewater treatment

This study focused on the diversity of bacterial communities from two series of two-stage constructed wetlands (CWs) treating tannery wastewater, under different hydraulic conditions. Series were separately planted with Typha latifolia and Phragmites australis in expanded clay aggregates and operated for 31 months. The effect of plant species, hydraulic loading and unit stage on bacterial communities was addressed through bacterial enumeration and denaturating gradient gel electrophoresis (DGGE). Diverse and distinct bacterial communities were found in each system unit, which was related in part to the type of plant and stage position (first or second unit in the series). Numerical analysis of DGGE profiles showed high diversity in each unit with an even distribution of species. No clear relation was established between the sample collection time, hydraulic loading applied and the bacterial diversity.     

The use of vertical flow constructed wetlands for on-site treatment of domestic wastewater: New Danish guidelines

Official guidelines for the on-site treatment of domestic sewage have recently been published by the Danish Ministry of Environment as a consequence of new treatment requirements for single houses and dwellings in rural areas. This paper summarises the guidelines for vertical constructed wetland systems (planted filter beds) that will fulfil demands of 95% removal of BOD and 90% nitrification. The system can be extended with chemical precipitation of phosphorus with aluminium polychloride in the sedimentation tank to meet requirements of 90% phosphorus removal. The necessary surface area of the filter bed is 3.2 m²/person equivalent and the effective filter depth is 1.0 m. The filter medium must be filtersand with a d₁₀ between 0.25 and 1.2 mm, a d₆₀ between 1 and 4 mm, and a uniformity coefficient (U = d₆₀/d₁₀) less than 3.5. The sewage is, after sedimentation, pulse-loaded onto the surface of the bed using pumping and a network of distribution pipes. The drainage layer in the bottom of the bed is passively aerated through vertical pipes extending into the atmosphere in order to improve oxygen transfer to the bed medium. Half of the nitrified effluent from the filter is recirculated to the first chamber of the sedimentation tank or to the pumping well in order to enhance denitrification and to stabilise the treatment performance of the system. A phosphorus removal system is installed in the sedimentation tank using a small dosing pump. The mixing of chemicals is obtained by a simple airlift pump, which also circulates water in the sedimentation tank. The vertical flow constructed wetland system is an attractive alternative to the common practice of soil infiltration and provides efficient treatment of sewage for discharge into the aquatic environment.     

Performances of constructed wetlands for municipal wastewater treatment in rural mountainous area

A global performance evaluation of an experimental Horizontal SubSurface Flow Constructed Wetlands (HSSF) was made after 6 years of functioning. This wetland is situated in French prealpine mountain, at 720 m elevation. The HSSF process treatment consists in a three-stage system dimensioned for 350 People Equivalent. Different helophytes were planted such as Typha latifolia, Phragmites australis and Scirpus maritimus. The mean hydraulic residence time for sewage was closed to 4–5 days, but in summer the mean pollutant residence time increases to 6 days due to an important evapotranspiration. There is no clogging of the gravel matrix and the hydraulic conductivity was very good and stabilized. Removal pollutant efficiency was determinate at each stages. There was a high removal of total suspended solids (TSS) all year around with an average of 95.6% (±3.6). More than 80% of removal occurred in the first stage. Physical processes (decantation, filtration) associated with biological oxidation were the principal factors of this removal. For COD and BOD₅, removal efficiency in the first stage were close to 60% on average and more than 90% at the outlet of the wetland. These results are similar to those observed with SSFW in many cases. Influence of temperature seems very weak because there were no significant seasonal variations of the process efficiency. Minimum effluent quality standards (30 mg l^–1 TSS; 120 mg l^–1 COD; 40 mg l^–1 BOD₅) were always respected. In cold periods, nutrients uptake was reduced but remained up to 60% in average. Mean bacterial removal efficiency was about two order of magnitude (99%) but can reach up to five order of magnitude in summer. These cyclic variations follow a sinusoidal variation around an annual mean. Pollutants removals were correlated to their respective loadings and no limits has been observed except for nitrogen. These results confirm that SSFW, an ecotechnology, should be considered as an alternative to conventional treatment methods (activated sludge, fixed biofilm) for small communities even in mountainous area.     

The performance of a multi-stage system of constructed wetlands for urban wastewater treatment in a semiarid region of SE Spain

This paper describes the results obtained in an experimental multi-stage system of created wetlands in Mojacar, in semiarid SE Spain, operating from June to October 1997. We compare the removal efficiency of four different series of treatments each consisting of three stages, using different flow rates of sewage, flow regimes, types of substrate and influents. Pretreated water from an anaerobic stabilization pond and treated water from the last pond of a lagoon system were used, the latter to test the system's suitability as a complementary system for removing nitrogen and phosphorus. In spite of the initial high wastewater concentrations, the effluent conforms to the strictest European norms (directive 91/271) for primary and secondary retention. A net treatment area of 2.3 m²/PE showed a high performance for SS (90–96%), COD (87%) and BOD₅ removal (90%) during the early stages of operation; however, nutrient removal was lower than was expected as compared with other studies. The addition of iron to the substrate improved phosphorus retention significantly (from 55 to 66%). The decrease of the net treatment area to 1.2 m²/PE did not significantly affect the wetland performance, with the exception of COD removal (78%). Series fed with treated water from the lagoon system (1.6 m²/PE) noticeably improved the quality of the effluent (average values of 7 mg/l total-N and 3 mg/l total-P).     

The role of constructed wetlands in secondary effluent treatment and water reuse in subtropical and arid Australia

Water reclamation and reuse is being actively promoted in Australia. In Queensland, surface-flow constructed wetlands with a diversity of macrophyte types offer the greatest potential for effluent polishing. Constructed wetlands in subtropical climates in coastal regions and arid climates in inland western regions are conducive to high macrophyte growth rates and nutrient removal, in particular nitrogen, producing an effluent suitable for irrigation, restoration of wetlands and/or release into natural waterways. Faecal-coliform removal is also high, producing effluent with <1000 cfu/100 mL and as low as 100 cfu/100 mL, acceptable for agricultural irrigation. Constructed wetlands can be designed to maximise the removal of both nutrients and pathogens by enhancing macrophyte diversity and natural disinfection processes by incorporating lagoons, shallow-water wetlands and subsurface-flow wetlands into the treatment train. Surface-flow wetlands can also be designed to minimise mosquito breeding by increasing macro-invertebrate predators, thereby alleviating community concerns about potential health risks. This paper addresses the role of constructed wetlands in nutrient and pathogen removal in Queensland's wetlands, and presents three case studies with respect to effluent reuse.     

Performance evaluation of eight years experience of constructed wetland systems in Catalonia as alternative treatment for small communities

In Catalonia (Spain), a variety of different systems have been built to naturally treat liquid residues from small communities. Some of these wastewater treatment plants (WWTPs) include constructed wetlands with horizontal subsurface flow (HSSF) as secondary treatment. The present study described and characterized the performance of 11 WWTPs with secondary HSSF constructed wetland systems after an initial operating period of 8 years. The effluent concentrations of Biochemical Oxygen Demand (BOD₅), Total Suspended Solids (TSS), Total Nitrogen (TN) and Total Phosphorous (TP) were statistically analyzed, and removal efficiencies for all WWTPs including all stages in treatment were calculated. The accumulated probability functions of those parameters were evaluated to determine the influence of two different types of polishing units on the overall performance: (a) only lagoon systems and (b) lagoon systems with HSSF. The statistical analysis indicates good performance for BOD₅ and TSS. In the first case, mean concentrations below 25 mg/L were found in 9 of the 11 plants analyzed and removal efficiencies between 78 and 96% were observed. In the second case, mean concentrations below 35 mg/L were found in 8 of the 11 plants, and removal efficiencies were between 65 and 88%. For the nutrients, the removal efficiency for TN and TP were in the range of 48-66% and 39-58%, respectively. Additionally, the analysis of the influence of the polishing units did not show a significant improvement (α > 0.05) for any parameter in the wetland systems without a subsequent polishing unit. However, in the wetland systems with a polishing unit of HSSF, a significant improvement (α < 0.05) was found for the effluent's BOD₅, TN and TP concentrations but with no significant contribution in TSS management.     

Microbial removal from the separated liquid fraction of anaerobically digested pig manure in meso-scale integrated constructed wetlands

The aim was to investigate microbial removal from the liquid fraction of anaerobically digested pig manure in meso-scale integrated constructed wetlands (ICW’s) over a 13 month period. Four treatments were investigated: T1 (standard), T2 (effluent recycling), T3 (high nutrient loading), and T4 (high flow rate). Mean counts of yeasts and moulds and spore-forming bacteria were higher in T3 and T4 than in T1 and T2 (P < 0.05). Flow through the cells reduced mean counts of coliform, yeasts and moulds and spore-forming bacteria across all treatments (P < 0.01). Counts varied with season; coliform were highest in the Summer (P < 0.001), with yeasts and moulds highest in the Summer and Autumn (P < 0.01) and spore-formers lowest in the Autumn (P < 0.001). As Salmonella was undetectable in the influent and Escherichia coli and Enterococcus were rarely detected it is difficult to make conclusions regarding pathogen removal. Further investigations using marked strains would allow pathogen tracking within the ICW’s.     

Constructed wetlands for the treatment of landfill leachates: The Slovenian experience

Constructed wetlands are widely recognized as an economical, efficient and environmentally acceptable means to treat many different types of wastewater. Six systems have been constructed in Slovenia for the treatment of landfill leachates. This paper describes the early stages of two treatment systems operating from 1990 to 1993 that were used to treat leachates from municipal landfills. System S1 consisted of a sedimentation lagoon and a 600 m² reed bed. System S2 was designed with a sedimentation lagoon and two reed beds (total=450 m²). The subsurface flow in both was horizontal and fluctuated widely in S2, but was a constant 0.2 1 s^–1 in S1. Peat, soil, sand and gravel were in system S2, while gravel with a hydraulic conductivity of 5×10^–4 m s^–1, was in S1.The unanticipated fluctuations of hydraulic and organic loadings influenced their performance. The efficiency in reduction of organic matter, N, P, metals and fecal coliforms varied through the year. In 3 years of operation, the average removal efficiencies for COD, BOD₅ and TSS were 38%, 61%, and 81%, respectively, in S1, and 53%, 45%, and 47%, respectively, in 1.5 years of operation for S2. The reduction of ammonium did not reach the effluent standard of 10 mg l^–1 for either S1 or S2. As, Zn, Pb, and Cu accumulated in roots, and Cu, Fe, As, Ni and Pb accumulated in rhizomes after one year of operation in S2.     

Isolation of Pseudomonas stutzeri in wastewater of catfish fish-ponds in the Mekong Delta and its application for wastewater treatment

The aim of this study was to explore the potential for reducing soluble N load in fishpond wastewater using naturally occurring denitrifying bacteria. Twenty-seven isolates were selected from in wastewater (liquid/solid) of catfish-ponds located along the Tien river, in the Mekong Delta, Vietnam in SW-LB medium (artificial seawater Luria-Britani medium) supplemented with 10 mM NH₄ and NO₃ and twenty-five isolates were identified as Pseudomonas stutzeri based on similarity of PCR-16S rRNA using universal primers and specific primers. Four isolates were effective in lowering soluble N (NH₄, NO₂ and NO₃) levels in fishpond water from 10 mg/L to negligible amounts after four days. Further experiments are underway to determine the fate of N lost from solution and the relative activity of ammonia oxidation, and nitrite and nitrate reduction by P. stutzeri isolates.     

Constructed wetlands for waste water treatment: the use of laterite in the bed medium in phosphorus and heavy metal removal

In Northern Ireland, phosphorus enrichment of lakes due to agriculture is a significant problem. Heavy metal exports from landfill sites, often located on water-logged land, are also of concern. Locally available laterite, a low grade bauxite which is rich in iron and aluminium, is used in acid solution with subsequent precipitation to remove phosphorus and heavy metals at several sewage treatment works. Constructed wetlands offer an attractive alternative to conventional waste water treatment in certain circumstances but removal of phosphorus is strongly dependent on the bed medium. Calcium-, iron- and aluminium-rich solid media are recommended. A brief introduction to the use and cost-effectiveness of constructed wetlands (CWs) in treating a range of effluents is given. This study, using both laboratory tests and pilot-scale constructed wetlands, reports the effectiveness of granular laterite in removing phosphorus and heavy metals from landfill leachate. Initial laboratory studies have shown that laterite is capable of 99% removal of phosphorus from solution. A pilot-scale experimental CW containing laterite achieved 96% removal of phosphorus. This removal is much greater than that reported in other systems. Initial removals of aluminium and iron by pilot-scale CWs have been up to 85% and 98% respectively. Percolating columns of laterite reduced Cd, Cr and Pb to undetectable concentrations. Possible application of this low cost, low technology, visually unobtrusive yet efficient system to rural areas with dispersed point sources of pollution is discussed.     

Panicum maximum (Jacq.) density effect upon macrofauna structure in sediments of pilot-scale vertical flow constructed wetlands treating domestic wastewater

Plant density may have an impact on macrofauna structure in constructed wetlands (CW). In this study, Panicum maximum density effect on macrofauna structure in pilot-scale vertical flow CW treating domestic wastewater was estimated. Two beds were planted with P. maximum at 10 roots/m² (low density) and two others at 20 roots/m² (high density). Two unplanted beds were used as controls. After six months of wastewater treatment, macrofauna was collected by taking five cores of sediment samples at the corners and the centre of each bed following three layers in the vertical profile. Plant density seems not to impact significantly the CW performance. However, the plant density of 10 roots/m² (low density) provided higher wastewater treatment efficiency. Concerning macrofauna, 11 taxa belonging to 6 classes and 11 orders were collected. Macrofauna was significantly more diversified in the planted beds than in the control. But the two plant densities investigated do not show significant difference between macrofauna diversity of the planted beds. Macrofauna abundance was two- and three-fold higher, respectively, in the planted beds at high and low densities than in the controls. From the upper surface to the bottom of the beds, macrofauna diversity and abundance decreased, and were heavily dominated by Annelida.     

The updated check list of Dolichopodidae (Diptera) of the Czech Republic and Slovakia: Background information,data and considerations

The 1997 check list of Dolichopodidae of the Czech Republic and Slovakia has recently been reviewed and updated. The new species list includes 346 species with 22 species added as new to the fauna of the Czech Republic. While the check list itself is published elsewhere, largely unpublished new records of Hercostomus argentifrons, H. nigrilamellatus, Medetera adjaniae, M. melancholica and M. setiventris are presented here, together with data on their distribution in Europe and their biology and ecology. The status of the newly added Sympycnus desoutteri is discussed. H. argentifrons is recorded here for the first time from the Czech Republic (Bohemia; Moravia) and background information is given on its discovery. While the Czech fauna with 324 species can be considered well known, the fauna of Slovakia is definitely much richer than its current national list of 217 species suggests. In the latter country, in particular surveys of sandy habitats with heathland or peatmoor, saltmarshes, reedmarshes, humid forests on loamy soils, and of rothole and saprun microhabitats on trees might quickly yield new species records.     

Metal retention and distribution in the sediment of a constructed wetland for industrial wastewater treatment

A free water surface wetland was built in 2002 to treat wastewater from a tool factory containing metals (Cr, Ni, Zn and Fe), nutrients and organic matter. Until 2006, the last reported period, the wetland retained metals and stored them primarily in the bottom sediment and in the biomass of macrophytes secondarily. The aim of this work was to study metal retention and distribution in the sediment of a constructed wetland for industrial wastewater treatment. Total concentrations and fractions (exchangeable, carbonate-bound, Fe-Mn oxides-bound, organic matter-bound and residual) of metals in sediment were analyzed in this treatment wetland, in order to estimate the fate of metals over time. Metal concentrations were significantly higher in the inlet than in the outlet sediment; concentrations in the latter remained without significant differences throughout the testing period. Metal concentrations and redox potential decreased with depth within the sediment. The lowest metal concentrations and pH and the highest redox values were attained in spring, in agreement with the period of maximum macrophyte growth. Ni and Zn were mainly stored associated with the carbonate fraction; Cr was mainly associated with the Fe-Mn oxides fraction, while Fe was mainly associated with the residual fraction, probably as pyrite. The incoming wastewater composition containing high pH, carbonate, calcium and Fe concentrations favored the observed association in the surface sediment. It would be expected that sediment will continue retaining metals in fractions that will not release them into the water while the chemical and environmental conditions remain unchanged.     

Origin and genetic structure of white-tailed sea eagles (<Emphasis Type="Italic">Haliaeetus albicilla</Emphasis>) in the Czech Republic: an analysis of breeding distribution,ringing data and DNA microsatellites

The population of white-tailed sea eagles (Haliaeetus albicilla) in the Czech Republic declined dramatically during the twentieth century. None were observed in the area for more than 60 years until population recoveries were observed beginning in the 1980s. It is currently estimated that 25–30 breeding pairs of white-tailed sea eagles nest in the Czech Republic. This article analyses surveillance data from three periods between 1973 and 2003 on the occurrence and nesting of white-tailed sea eagles in the Czech Republic. We investigated recolonization of European white-tailed sea eagles in the Czech Republic in terms of migration patterns and population structures. Bird ringing data suggest the Czech population may be recovered from various areas encompassing northern Europe. Using data collected by DNA microsatellite, no population structure was revealed through Bayesian and cluster analyses with an existing Hardy–Weinberg equilibrium, which suggests mixed panmictic populations of white-tailed sea eagles in the Czech Republic and Slovakia. While analysis of genetic diversity showed no difference between recovered populations in the southeastern Czech Republic and those persisting in Slovakia, there was genetic diversity between eagles of the southeastern subpopulation and eagles in other parts of the Czech Republic. Taken together, these observations on the population structure of white-tailed sea eagles in the Czech Republic imply that other European birds contributed to the recovery of the Czech population, likely through breeding mixture with an identifiable centre in the southeastern Czech Republic.