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.     

Biodiversity of constructed wetlands for wastewater treatment

Constructed wetlands are often built for wastewater treatment to mitigate the adverse effects of organic pollution in streams and rivers caused by inputs of municipal wastewater. However, there has been little analysis of biodiversity and related factors influencing the ecosystem functioning of constructed wetlands. The purpose of this study was to evaluate the biodiversity of two free-water-surface integrated constructed wetlands in subtropical Taiwan by analyzing the water quality, habitat characteristics, and biotic communities of algae, macrophytes, birds, fish, and aquatic macroinvertebrates in the treatment cells. Our results indicated that the two integrated constructed wetlands (Hsin-Hai II and Daniaopi Constructed Wetlands) achieved good performance in reducing the concentrations of total nitrogen (TN) and total phosphorus (TP), and loadings of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) from municipal sewage. In total, 58 bird species, 7 fish species, and 34 aquatic macroinvertebrate taxa were recorded in the two wetlands. The results of stepwise multiple regressions showed that the richness, abundance, and diversity of birds increased with wetland area. Fish richness and abundance respectively increased with wetland area and dissolved oxygen, while the diversity decreased with increases in TP concentrations. The richness and density of aquatic macroinvertebrates increased with the cover of aquatic macrophytes, while the diversity increased with wetland area. Ordination analyses indicated that variations in the community structures of birds, fishes, and aquatic macroinvertebrates were respectively best explained by water temperature, wetland area, and species richness of fish. Our results suggest that wetland area, cover of aquatic macrophytes, and water quality were the most important factors governing the diversity in the constructed wetlands, and that the factors influencing community structures varied among different taxonomic groups. In addition to improving water quality, this study implied that the biodiversity of constructed wetlands for wastewater treatment can be enhanced through proper design and management.     

Phragmites australis and silica cycling in tidal wetlands

Tidal marshes have recently been shown to be important biogenic Si recycling surfaces at the land–sea interface. The role of vegetation in this recycling process has not yet been quantified. In situ and ex situ decomposition experiments were conducted with Phragmites australis stems. In a freshwater tidal marsh, litterbags were incubated at different elevations and during both winter and summer. Biogenic Si (BSi) dissolution followed a double exponential decay model in the litterbags (from ca. 60 to 15 mg g⁻¹ after 133 days), irrespective of season. Si was removed much faster from the incubated plant material compared to N and C, resulting in steadily decreasing Si/N and Si/C ratios. Ex situ, decomposition experiments were conducted in estuarine water, treated with a broad-spectrum antibiotic, and compared to results from untreated incubations. The bacterial influence on the dissolution of dissolved Si (DSi) from P. australis stems was negligible. Although the rate constant for dissolved Si dissolution decreased from 0.004 to 0.003 h⁻¹, the eventual amount of BSi dissolved and saturation concentration in the incubation environment were similar in both treatments. P. australis contributes to and enhances dissolved Si recycling capacity of tidal marshes: in a reed-dominated small freshwater tidal marsh, more than 40% of DSi export was attributable to reed decomposition. As the relation between tidal marsh surface and secondary production in estuaries has been linked to marsh Si cycling capacity, this provides new insight in the ecological value of the common reed.     

Effects of plants and microorganisms in constructed wetlands for wastewater treatment

Constructed wetlands are a natural alternative to technical methods of wastewater treatment. However, our understanding of the complex processes caused by the plants, microorganisms, soil matrix and substances in the wastewater, and how they all interact with each other, is still rather incomplete. In this article, a closer look will be taken at the mechanisms of both plants in constructed wetlands and the microorganisms in the root zone which come into play when they remove contaminants from wastewater. The supply of oxygen plays a crucial role in the activity and type of metabolism performed by microorganisms in the root zone. Plants' involvement in the input of oxygen into the root zone, in the uptake of nutrients and in the direct degradation of pollutants as well as the role of microorganisms are all examined in more detail. The ways in which these processes act to treat wastewater are dealt with in the following order: Technological aspects; The effect of root growth on the soil matrix; Gas transport in helophytes and the release of oxygen into the rhizosphere; The uptake of inorganic compounds by plants; The uptake of organic pollutants by plants and their metabolism; The release of carbon compounds by plants; Factors affecting the elimination of pathogenic germs.     

Trace elements removal ability and antioxidant activity of Phragmites australis (from Algeria)

Abstract

In this study, roots, stems and leaves of the worldwide distributed macrophyte Phragmites australis (common reed) were tested as potential removal and biomonitors of trace elements contamination in sediment. In particular, the concentrations (100, 200, and 500?mg/kg) of the following elements were analyzed: Zn, Cu, Pb, and Fe. Results showed that the amount of concentrations in plant tissues is significantly (p?≤?0.01) dependent on the kind of organ and element. Trace element concentrations decreased according to the pattern of Fe^a (Roots^a > Stems^b > Leaves^b) > Zn^b (Root^a > Leaves^b > Stems^c) > Cu^c (Roots^a > Leaves^b > Stems^c) > Pb^c (Roots^a > Stems^b > Leaves^c), as well as the roots acted as the main centers of bioaccumulation for all elements studied, and stems as the transit organs for translocation from roots to leaves. The major mechanisms employed by the plant were probably phytostabilization on the basis of the calculated Biological Concentration Factor (BCF – metal concentration ratio of plant root to soil); and Translocation Factor (TF – metal concentration ratio of plants roots to above ground part). Finally, due to the low scavenger effect of the radical DPPH, we excluded the hypothesis of the use of antioxidant mechanism in the tolerance of metals.     

Horizontal subsurface flow constructed wetlands for tertiary treatment of dairy wastewater

The aim of this work was to evaluate the efficiency of horizontal subsurface flow constructed wetlands (HSFCWs) planted with Typha domingensis and Phragmites australis in the final treatment of dairy wastewater. Ten microcosms-scale reactors simulating HSFCWs were arranged outdoors under a semi-transparent plastic roof. Five replicates were planted with T. domingensis and five with P. australis. In both cases, light expanded clay aggregate (LECA) 10/20 was used as a substrate. Real effluent with previous treatment was used. In order to evaluate contaminant removal efficiencies in each reactor, pH, electrical conductivity, suspended solids, ammonium, nitrate, nitrite, total phosphorus, and chemical oxygen demand (COD) were analyzed before and after treatment. HSFCWs planted with T. domingensis and P. australis were efficient for the final treatment of dairy wastewater. Removal efficiencies obtained in microcosms planted with both macrophytes were over 96% for ammonium and nitrite. Nitrate removal efficiency was 39%. COD decreased along the experiment near 75% for both treatments. High removal percentages for suspended solids (78.4–81.1%) were also achieved. However, systems planted with T. domingensis were significantly more efficient for total phosphorus removal (88.5%) than those planted with P. australis (71.6%).     

Municipal wastewater treatment with vertical flow constructed wetlands for irrigation reuse

The treatment effect of two pilot-scale vertical flow constructed wetlands (VFCWs) on municipal wastewaters and their suitability for irrigation reuse were evaluated in a 2-year (2002–2003) experiment. One VFCW was planted with Typha latifolia and the other with Phragmites australis. VFCW efficiency was evaluated in terms of both mass removal and water quality improvement, considering the following parameters: pH, electrical conductivity (EC_w), total suspended solids (TSS), chemical oxygen demand (COD) and biochemical oxygen demand (BOD), total nitrogen (TN) and nitrate (NO₃^?), total phosphorus (TP) and orthophosphate (PO₄^3?), sodium (Na), potassium (K), magnesium (Mg) and calcium (Ca). The accumulation of the elements in the plant organs and VFCW sandy surface layer and their offtake with the macrophyte harvest were also measured.In quantitative terms the established VFCWs showed higher removal efficiencies (>86%) for COD, BOD, N and K, while lower efficiencies (<47%) were observed for Na and Mg. The direct contribution (offtake) of the macrophytes in N, P and K removal processes was particularly high (>65%) due to the massive growth. The results were less favourable in terms of water quality, because the high evapotranspiration losses counteracted the depuration process by concentrating the elements in the outflow water. Higher concentrations were found in outflow than inflow, especially of Na (relative increase of 89%) and Mg (relative increase of 74%). Only parameters with high removal efficiencies fulfilled the Italian guidelines for irrigation reuse whereas parameters with lower efficiencies (e.g., TSS, TP) limited the potential water reuse. Efficient pre-cleaning systems or innovative integrated systems are thus necessary to obtain high removal efficiencies that reduce the effect of ET on water quality.     

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.     

Hybrid constructed wetlands for wastewater treatment and reuse in the Canary Islands

The performance of two substrates commonly available in the zone, gravel and lapilli, was tested for their use in hybrid constructed wetland pilot plants for the treatment and reuse of urban wastewater in Gran Canaria, Canary Islands, Spain. The first stage of the systems was a vertical subsurface-flow constructed wetland and the second stage was a horizontal subsurface-flow constructed wetland. Parallel experiments were carried out with one system containing only crushed stone basaltic gravel as substrate and the other with only lapilli, a very porous volcanic sediment. The comparative effect of substrate type, hydraulic loading rate and planting was studied.Tracer studies indicated that the experimental TRHs were significantly lower than the theoretical ones, particularly for the vertical flow with gravel. Though the vertical flow with lapilli performed better than the one with gravel, the hybrids showed quite similar removals.Planting or varying the hydraulic loading rate introduced little differences between the vertical flows or the hybrids. Average removals for the gravel-based hybrid constructed wetland were 86% for BOD, 80% for COD, 88% for ammonia-N, 96% for SS and turbidity, 24% for phosphate-P, and 99.5% for faecal coliforms and 99.7% for faecal enterococci. Thus, it can be concluded that hybrid constructed wetlands proved to be robust configurations for wastewater treatment in the Canary Islands.     

扎龙芦苇湿地生长季的甲烷排放通量

为研究高寒地区天然淡水芦苇湿地的甲烷排放特征,采用静态箱-气相色谱法,测定了扎龙不同水位芦苇湿地生长季的甲烷排放通量.结果表明:观测期内,扎龙芦苇湿地甲烷排放通量平均为7.67 mg·m^-2·h^-1（-21.18～46.15 mg·m^-2·h^-1）,其中深水区(平均水深100 cm)和浅水区(平均水深25 cm)的平均甲烷排放通量分别为5.81和9.52 mg·m^-2·h^-1,排放峰值分别出现在8月和7月,最低值均出现在10月.深水区夏季(6-7月)的甲烷排放通量显著低于浅水区,而春(5月)、秋(8-10月)季节显著高于浅水区.生长季甲烷排放通量的变化为夏季>秋季>春季;昼夜排放量为12:00和14:00最高,0:00最低.温度和水位是高寒地区淡水芦苇湿地甲烷排放通量变化的主要影响因子.     

Rehabilitation by constructed wetlands of available wastewater treatment plant in Sakhnin

In rural areas, insufficient wastewater treatment often causes serious environmental problems, especially for human health. Due to this problem, new wastewater treatment plants (WWTP) should be constructed or upgraded. When considering economic and maintenance factors, constructed wetlands (CWs) are more desirable processes. The available WWTP located in the Northern Israeli town of Sakhnin was redesigned and upgraded. To rehabilitate the WWTP, six new CWs having different operating conditions were constructed as a pilot project. The most appropriate place of construction of the CWs was thought to be at the end of the WWTP. From the beginning of the system, inlet and outlet pollution parameters such as chemical oxygen demand (COD), ammonia (NH₄-N⁺), total suspended solids (TSS), and phosphorus (PO₄-P³⁻) were monitored in the CWs from August 2005 to February 2006. As a result the most appropriate CWs were found having Phragmites as plant and volcanic tufa as media material. The maximum removal efficiencies were 71.8% on COD, 92.9% on TSS, 63.8% on ammonia for CW5 tank. Adversely, phosphorus removal was not so high in CW5. Phosphorus removal was negligible in the study.     

人工湿地污水处理技术问题及改进措施研究进展

人工湿地作为一种绿色生态、低成本的污水处理技术,其应用日渐广泛。随着应用和机理研究的深入,传统湿地在运行过程中也涌现出各种问题。本文总结了近几年来人工湿地污水处理所出现的堵塞、脱氮效率低、污染负荷小、受温度影响大等问题,综述了国内外学者针对这些问题采取的内部系统强化、工艺改进以及与其他工艺类型组合等措施,并对今后人工湿地技术的发展方向进行探讨。     

人工湿地处理造纸废水后细菌群落结构变化

人工湿地通过模拟自然湿地的生态系统,能够实现污染物的去除,是一种高效经济的污水处理手段,但是对人工湿地处理后污水中细菌群落的研究较少。采集了造纸厂排污口和人工湿地出水口的水样,检测了溶解氧、pH值和盐度等水质指标,对主要污染物的含量进行了测定和分析,并利用DGGE技术对细菌群落的变化进行了研究。结果表明:(1)造纸污水经人工湿地处理后水质有明显提高;(2)人工湿地处理后细菌群落结构发生变化,优势菌由γ变形菌和衣原体变为α变形菌,而且微生物多样性指数Shannon-Wiener's降低;(3)人工湿地处理前污水中存在着大量致病微生物和降解微生物,处理后以环境友好的固氮菌和少量致病菌为主。研究结果揭示了人工湿地不仅可以去除造纸废水中的污染物,改善水质而且可以大大减少向环境中排放的致病微生物,防止由致病微生物引起的生态灾难的发生,为将来人工湿地应用于工业污水处理和微生物生态安全评估提供有效可靠的依据。     

Common reed (Phragmites australis) invasion and amphibian distribution in freshwater wetlands

Invasive plants can substantially modify wetland structure and animal distribution patterns. In eastern North America, a Eurasian haplotype of the common reed (Phragmites australis, haplotype M) is invading wetlands. We studied the invasion of common reed in freshwater wetlands of an urbanized landscape and its effects on the distribution of amphibians at different life stages. Specifically, we hypothesized that the probability of reed invasion would be greatest in wetlands near anthropic disturbances. We predicted that the probability of desiccation at sampling stations increases with reed cover. Furthermore, we expected that wetlands invaded by common reed would have lower amphibian abundances, apparent survival, and rates of recruitment. We conducted trapping surveys to compare anuran assemblages of tadpoles, juveniles, and adults in 50 wetlands during two field seasons. The probability of reed invasion in wetlands increased with the cover of heavily-managed areas within 1,000 m and the distance to the nearest forest, but decreased with the length of roads within 1,000 m. The probability of station desiccation increased with reed cover. We found no evidence of a negative effect of reed presence on anuran population parameters, at any life stage. Landscape variables, such as the percent cover of forest or heavily-managed areas within a given radius from each wetland, influenced the abundance or the apparent survival of juvenile frogs and the abundance of ranid tadpoles. Our results show that amphibian patterns depend more strongly on the structure of the landscape surrounding wetlands than on exotic reed invasion in wetlands.     

Freshwater wetlands: fertile grounds for the invasive Phragmites australis in a climate change context

Climate change will likely affect flooding regimes, which have a large influence on the functioning of freshwater riparian wetlands. Low water levels predicted for several fluvial systems make wetlands especially vulnerable to the spread of invaders, such as the common reed (Phragmites australis), one of the most invasive species in North America. We developed a model to map the distribution of potential germination grounds of the common reed in freshwater wetlands of the St. Lawrence River (Québec, Canada) under current climate conditions and used this model to predict their future distribution under two climate change scenarios simulated for 2050. We gathered historical and recent (remote sensing) data on the distribution of common reed stands for model calibration and validation purposes, then determined the parameters controlling the species establishment by seed. A two‐dimensional model and the identified parameters were used to simulate the current (2010) and future (2050) distribution of germination grounds. Common reed stands are not widespread along the St. Lawrence River (212 ha), but our model suggests that current climate conditions are already conducive to considerable further expansion (>16,000 ha). Climate change may also exacerbate the expansion, particularly if river water levels drop, which will expose large bare areas propitious to seed germination. This phenomenon may be particularly important in one sector of the river, where existing common reed stands could increase their areas by a factor of 100, potentially creating the most extensive reedbed complex in North America. After colonizing salt and brackishwater marshes, the common reed could considerably expand into the freshwater marshes of North America which cover several million hectares. The effects of common reed expansion on biodiversity are difficult to predict, but likely to be highly deleterious given the competitiveness of the invader and the biological richness of freshwater wetlands.     

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.     

Designing constructed wetlands for reclamation of pretreated wastewater and stormwater

Wastewater reclamation is getting greater attention as an alternative to conventional approaches to wastewater treatment and water supply due to increasing water stress coupled with more stringent water quality limitation for discharge of treated wastewater. Among the few technologies adopted in the field for wastewater reclamation, constructed wetlands have been used to reclaim both primary and secondary treated wastewater in regions with arid and humid climates. This paper summarizes the widely adopted guidelines that need to be considered when designing constructed wetlands for wastewater reclamation, discusses the capacity of wetland treatment systems for water reuse while assessing the status of full-scale constructed wetlands designed for wastewater reclamation, and develops contaminant loading charts as a design tool based on the performance of existing full-scale constructed wetlands deployed for wastewater reclamation. It is evident that constructed wetland systems provide a viable means to treat wastewater to the levels required for low-quality reuses such as restricted irrigation and impoundment. It is challenging for constructed wetlands to consistently meet microbiological guidelines for high-quality reuses such as unrestricted agricultural and urban reuses. Wastewater reclaimed through constructed wetlands is used mainly for agricultural and landscape irrigation, groundwater recharge, indirect potable reuse, and environmental reuse. Surface area and hydraulic loading rate of constructed wetlands to be deployed for wastewater reclamation can be estimated with contaminant loading charts derived from monitoring data of existing full-scale operations.     

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.     

Constructed wetlands for wastewater treatment

The first experiments using wetland macrophytes for wastewater treatment were carried by out by Käthe Seidel in Germany in early 1950s. The horizontal sub-surface flow constructed wetlands (HF CWs) were initiated by Seidel in the early 1960s and improved by Reinhold Kickuth under the name Root Zone Method in late 1960s and early 1970s and spread throughout Europe in 1980s and 1990s. However, cohesive soils proposed by Kickuth got clogged very quickly because of low hydraulic permeability and were replaced by more porous media such as gravel in late 1980s in the United Kingdom and this design feature is still used. In fact, the use of porous media with high hydraulic conductivity was originally proposed by Seidel. HF CWs provide high removal of organics and suspended solids but removal of nutrients is low. Removal of nitrogen is limited by anoxic/anaerobic conditions in filtration beds which do not allow for ammonia nitrification. Phosphorus removal is restricted by the use of filter materials (pea gravel, crushed rock) with low sorption capacity. Various types of constructed wetlands may be combined in order to achieve higher treatment effect, especially for nitrogen. However, hybrid systems are comprised most frequently of vertical flow (VF) and HF systems arranged in a staged manner. HF systems cannot provide nitrification because of their limited oxygen transfer capacity. VF systems, on the other hand, do provide a good conditions for nitrification but no denitrification occurs in these systems. In hybrid systems (also sometimes called combined systems) the advantages of the HF and VF systems can be combined to complement processes in each system to produce an effluent low in BOD, which is fully nitrified and partly denitrified and hence has a much lower total-N outflow concentrations.     

人工湿地处理炼油废水的生态效益研究

来自茂名石化公司的炼油废水含有较高浓度的污染物 ,超过广东省规定的排放标准 ,未经处理不能直接排放。 4种草本植物 ,香根草、芦苇、宽叶香蒲和蒲草被用来测试建植人工湿地的效果以及所建植的人工湿地处理炼油废水的效果。在为期 2个月的处理过程中 ,人工湿地在前期对炼油废水的净化效率很高 ,它们对第一批高浓度废水中氨氮、COD、BOD和油的去除率分别是 97.7%、78.2 %、91 .4%和 95 .3% ,对第一批低浓度污水分别是 97.1 %、71 .5 %、73.7%和 89.8%。但是 ,随着时间的推移 ,湿地的净化效果会有一定程度的下降 ,然后逐渐趋于稳定。湿地对氨氮、COD、BOD和油类的去除效率始终表现为氨氮 >油类 >BOD>COD,但植物对它们的净去除量却是 COD>BOD>氨氮和油类。湿地建植之初 ,植物的净化功能很弱 ,但随植物的生长和生物量的增加而逐渐增强。然而 ,不同植物种对废水的净化率很接近 ,基本上无显著性差异。被测试的 4种植物在污水湿地中的生长表现都好过在清水湿地中的 ,但香根草、芦苇和宽叶香蒲在高浓度废水的分蘖数比在低浓度的废水少些 ,而蒲草相反 ,表明高浓度污水相对于低浓度污水而言已经对前面 3个种产生了伤害 ,却仍促进蒲草生长。在清水培养阶段 ,香根草产生分蘖的速度是 4个种中最低的 ;进入污水培养阶