人工湿地植物研究进展

人工湿地具有去除污染效果好、运行费用低和易维护等特点,已被广泛用于污水处理中.湿地植物在其中起着重要作用,主要包括直接吸收氮、磷等污染物,通过根系输氧促进根区的氧化还原反应与好氧微生物活动及增强和维持介质的水力传输等.综述了人工湿地植物的去污机理,阐述了湿地植物对生物可降解的有机物、营养性污染物和有毒有害物质净化的研究成果与应用,并展望今后进一步研究的重点.     

Geochemical and mineralogical characterization of a neutral, low-sulfide/high-carbonate tailings impoundment, Markušovce, eastern Slovakia

Tailings deposits generated from mining activities represent a potential risk for the aquatic environment through the release of potentially toxic metals and metalloids occurring in a variety of minerals present in the tailings. Physicochemical and mineralogical characteristics of tailings such as total concentrations of chemical elements, pH, ratio of acid-producing to acid-neutralizing minerals, and primary and secondary mineral phases are very important factors that control the actual release of potentially toxic metals and metalloids from the tailings to the environment. The aims of this study are the determination of geochemical and mineralogical characteristics of tailings deposited in voluminous impoundment situated near the village of Marku?ovce (eastern Slovakia) and identification of the processes controlling the mobility of selected toxic metals (Cu, Hg) and metalloids (As, Sb). The studied tailings have unique features in comparison with the other tailings investigated previously because of the specific mineral assemblage primarily consisting of barite, siderite, quartz, and minor sulfides. To meet the aims, samples of the tailings were collected from 3 boreholes and 15 excavated pits and subjected to bulk geochemical analyses (i.e., determination of chemical composition, pH, Eh, acid generation, and neutralization potentials) combined with detailed mineralogical characterization using optical microscopy, X-ray diffraction (XRD), electron microprobe analysis (EMPA), and micro-X-ray diffraction (μ-XRD). Additionally, the geochemical and mineralogical factors controlling the transfer of potentially toxic elements from tailings to waters were also determined using short-term batch test (European norm EN 12457), sampling of drainage waters and speciation–equilibrium calculations performed with PHREEQC. The tailings mineral assemblage consists of siderite, barite, quartz, and dolomite. Sulfide minerals constitute only a minor proportion of the tailings mineral assemblage and their occurrence follows the order: chalcopyrite?>?pyrite?>?tetrahedrite?>?arsenopyrite. The mineralogical composition of the tailings corresponds well to the primary mineralization mined. The neutralization capacity of the tailings is high, as confirmed by the values of neutralization potential to acid generation potential ratio, ranging from 6.7 to 63.9, and neutral to slightly alkaline pH of the tailings (paste pH 7.16–8.12) and the waters (pH 7.00–8.52). This is explained by abundant occurrence of carbonate minerals in the tailings, which readily neutralize the acidity generated by sulfide oxidation. The total solid-phase concentrations of metal(loid)s decrease as Cu?>?Sb?>?Hg?>?As and reflect the proportions of sulfides present in the tailings. Sulfide oxidation generally extends to a depth of 2 m. μ-XRD and EMPA were used to study secondary products developed on the surface of sulfide minerals and within the tailings. The main secondary minerals identified are goethite and X-ray amorphous Fe oxyhydroxides and their occurrence decreases with increasing tailings depth. Secondary Fe phases are found as mineral coatings or individual grains and retain relatively high amounts of metal(loid)s (up to 57.6 wt% Cu, 1.60 wt% Hg, 23.8 wt% As, and 2.37 wt% Sb). Based on batch leaching tests and lysimeter results, the mobility of potentially toxic elements in the tailings is low. The limited mobility of metals and metalloids is due to their retention by Fe oxyhydroxides and low solubilities of metal(loid)-bearing sulfides. The observations are consistent with PHREEQC calculations, which predict the precipitation of Fe oxyhydroxides as the main solubility-controlling mineral phases for As, Cu, Hg, and Sb. Waters discharging from tailings impoundment are characterized by a neutral to slightly alkaline pH (7.52–7.96) and low concentrations of dissolved metal(loid)s (<5–7.0 μg/L Cu, <0.1–0.3 μg/L Hg, 5.0–16 μg/L As, and 5.0–43 μg/L Sb). Primary factors influencing aqueous chemistry at the site are mutual processes of sulfide oxidation and carbonate dissolution as well as precipitation reactions and sorption onto hydrous ferric oxides abundantly present at the discharge of the impoundment waters. The results of the study show that, presently, there are no threats of acid mine drainage formation at the site and significant contamination of natural aquatic ecosystem in the close vicinity of the tailings impoundment.     

Environmental behavior of explosives in groundwater from the Milan Army Ammunition Plant in aquatic and wetland plant treatments. Removal, mass balances and fate in groundwater of TNT and RDX.

Phytoremediation of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in groundwater using constructed wetlands is a potentially economical remediation alternative. To evaluate Explosives removal and fate was evaluated using hydroponic batch incubations of plant and substrate treatments with explosives-contaminated groundwater amended with [U-14C]-TNT or [U-14C]-RDX. Plants and substrates were collected from a small-scale wetland constructed for explosives removal, and groundwater originated from a local aquifer at the Milan Army Ammunition Plant. The study surveyed three aquatic, four wetland plant species and two substrates in independent incubations of 7 days with TNT and 13 days with RDX. Parent compounds and transformation products were followed using 14C and chemical (HPLC) analyses. Mass balance of water, plants, substrates and air was determined. It was demonstrated that TNT disappeared completely from groundwater incubated with plants, although growth of most plants except parrot-feather was low in groundwater amended to contain 1.6 to 3.4 mg TNT L-1. Highest specific removal rates were found in submersed plants in water star-grass and in all emergent plants except wool-grass. TNT declined less with substrates, and least in controls without plants. Radiolabel was present in all plants after incubation. Mineralization to 14CO2 was very low, and evolution into 14C-volatile organics negligible. RDX disappeared less rapidly than TNT from groundwater. Growth of submersed plants was normal, but that of emergent plants reduced in groundwater amended to contain 1.5 mg RDX L-1. Highest specific RDX removal rates were found in submersed plants in elodea, and in emergent plants in reed canary grass. RDX failed to disappear with substrates. Mineralization to 14CO2 was low, but relatively higher than in the TNT experiment. Evolution into 14C-volatile organics was negligible. Important considerations for using certain aquatic and wetland plants in constructed wetlands aimed at removing explosives from water are: (1) plant persistence at the explosives level to which it is exposed, (2) specific plant-mass based explosives removal rates, (3) plant productivity, and (4) fate of parent compounds and transformation products in water, plants, and sediments.     

Effects of taxonomy,sediment, and water column on C:N:P stoichiometry of submerged macrophytes in Yangtze floodplain shallow lakes,China

Carbon (C), nitrogen (N) and phosphorus (P) are the three most important essential elements limiting growth of primary producers. Submerged macrophytes generally absorb nutrients from sediments by root uptake. However, the C:N:P stoichiometric signatures of plant tissue are affected by many additional factors such as taxonomy, nutrient availability, and light availability. We first revealed the relative importance of taxonomy, sediment, and water column on plant C:N:P stoichiometry using variance partitioning based on partial redundancy analyses. Results showed that taxonomy was the most important factor in determining C:N:P stoichiometry, then the water column and finally the sediment. In this study, a significant positive relationship was found between community C concentration and macrophyte community biomass, indicating that the local low C availability in macrophytes probably was the main reason why submerged macrophytes declined in Yangtze floodplain shallow lakes. Based on our study, it is suggested that submerged macrophytes in Yangtze floodplain shallow lakes are primarily limited by low light levels rather than nutrient availability.

     

Effects of an industrial effluent on plant colonization and on the germination and post-germinative growth of seeds of terrestrial and aquatic plant species

Major oil sands industrial companies are located in the Athabasca Oil Sands Deposit in northeastern Alberta, Canada. During the process used to extract light crude oil (via hot water digestion and flotation), gypsum is usually added to produce consolidated tails (CT) and CT release water. The vast volumes of process-treated waters (effluent) are held within large dyked tailings ponds. Toward testing viable options for reclamation, various hummock-wetlands systems have been constructed; in addition, natural wetlands (inhabited by obligate wetland plant species) have become established as a result of seeping of the effluents held within the large dyked ponds. Vegetation surveys conducted on and around the industrial site revealed that the constructed wetlands associated with the dyke drainage (effluent treated with phosphorous) and consolidated tails (CT; effluent treated with gypsum) had low biodiversity and were not invaded by many aquatic plants. Although the natural wetland was also not invaded by many aquatic species, it was found to be as diverse as the reference wetlands (i.e. off-site wetlands not exposed to the effluents). Exposure to oil sands effluents had an inhibitory effect on the germination (percent and/or rate) of several plant species (tomato, clover, wheat, rye, pea, reed canary grass, loblolly pine); clover and tomato seed germination were most affected. Two treatments in particular (effluents from the natural on-site wetland and the CT constructed wetland), delayed germination, and also led to reduced fresh weight of seedlings of tomato, wheat, clover and loblolly pine. The osmolarities of the effluents associated with the natural on-site wetland and CT constructed wetland were 712 and 728 mOs/kg, respectively; substituting these effluents with solutions of polyethylene glycol of the same osmotic potentials had a greater inhibitory effect on germination rate. The negative effects of the effluents on seed germination may account for the paucity of aquatic species that invaded the oil sands impacted wetlands. This factor will also be critical in determining the long-term feasibility of hummock-wetland systems.     

The effect of pH on plant litter decomposition and metal cycling in wetland mesocosms supplied with mine drainage

The long term effectiveness of compost-based wetland systems treating net-acidic mine waters is reliant upon a continuing supply of decomposed organic matter which provides the basic foodstock for sulphate reducing bacteria. The annual turnover of wetland vegetation within these systems has been suggested to be the primary source for this material once the original substrate has been consumed. This study aimed to determine whether plant litter (of Common Reed, Phragmites australis) decomposition rates and release of metals and nutrients were affected by pH using controlled experiments under laboratory conditions. Loss of plant biomass was found to be unaffected by pH (3.0-6.5) suggesting that plant litter could be an important source of organic molecules for bacterial populations even under acidic conditions. The decomposing plant litter also acted as a focus for the precipitation of Fe oxides and sorption of Zn thereby acting as a short-term sink for these contaminants. This has important implications for geochemical cycling within the wetland system and potential transport out of the system. The essential nutrients (K and Mg) released from plant litter were affected by pH which could be important in nutrient availability for re-use by vegetation and other organisms within the system.     

Dynamics of metal tolerant plant communities' development in mine tailings from the Cartagena-La Unión Mining District (SE Spain) and their interest for further revegetation purposes

Mine tailings are typical elements in post-mining landscapes which usually have high heavy metal contents and are affected by intensive erosion processes, above all in arid and semiarid areas. Revegetation of these sites is considered a low cost and suitable technology to effect surface stabilization. Spontaneous plant communities that colonize tailings in Southern Spain showed different behavior depending on the pH: in neutral tailings the plant communities were formed by less number of plant species than in acid tailings but they had less seasonal variations, showing a stable development. This spontaneous vegetation, that is adapted to metal toxicity and to drought, allows reducing air borne and water erosion, and may mitigate the spread of the contamination to the nearby areas.     

Effects of macrophytes and external carbon sources on nitrate removal from groundwater in constructed wetlands

Several microcosm wetlands unplanted and planted with five macrophytes (Phragmites australis, Commelina communis, Penniserum purpureum, Ipomoea aquatica, and Pistia stratiotes) were employed to remove nitrate from groundwater at a concentration of 21-47 mg NO3-N/l. In the absence of external carbon, nitrate removal rates ranged from 0.63 to 1.26 g NO3-N/m2/day for planted wetlands. Planted wetlands exhibited significantly greater nitrate removal than unplanted wetlands (P<0.01), indicating that macrophytes are essential to efficient nitrate removal. Additionally, a wetland planted with Penniserum showed consistently higher nitrate removal than those planted with the other four macrophytes, suggesting that macrophytes present species-specific nitrate removal efficiency possibly depending on their ability to produce carbon for denitrification. Although adding external carbon to the influent improved nitrate removal, a significant fraction of the added carbon was lost via microbial oxidation in the wetlands. Planting a wetland with macrophytes with high productivity may be an economic way for removing nitrate from groundwater. According to the harvest result, 4-11% of nitrogen removed by the planted wetland was due to vegetation uptake, and 89-96% was due to denitrification.     

Degradation of 2,4,6-trinitrotoluene by selected helophytes

Four emergent plants (helophytes, synonyms emersion macrophytes, marsh plants, etc.) Phragmites australis, Juncus glaucus, Carex gracillis and Typha latifolia were successfully used for degradation of TNT (2,4,6-trinitrotoluene) under in vitro conditions. The plants took up and transformed more than 90% of TNT from the medium within ten days of cultivation. The most efficient species was Ph. australis which took up 98% of TNT within ten days. The first stable degradation products 4-amino-2,6-dinitrotoluene (4-ADNT) and 2-amino-4,6-dinitrotoluene (2-ADNT) were identified and analysed during the cultivation period. [14C] TNT was used for the detection of TNT degradation products and their compartmentalization in plant tissues after two weeks of cultivation. Forty one percent of 14C was detected as insoluble or bound in cell structures: 34% in roots and 8% in the aerial parts. These results open the perspective of using the above-mentioned plants for the remediation of TNT contaminated waters.     

Shade and flow effects on ammonia retention in macrophyte-rich streams: implications for water quality

Controlled releases of NH4-N and conservative tracers (Br- and Cl-) to five reaches of four streams with contrasting macrophyte communities have shown differing retentions, largely as a result of the way plants interact with stream flow and velocity. First-order constants (k) were 1.0-4.8 d(-1) and retention of NH4-N was 6-71% of amounts added to each reach. Distance travelled before a 50% reduction in concentration was achieved were 40-450 m in three streams under low-flow conditions, and 2400-3800 m at higher flows. Retention (%) of NH4-N can be approximated by a simple function of travel time and k, highlighting the importance of the relationship between macrophytes and stream velocity on nutrient processing. This finding has significant management implications, particularly with respect to restoration of riparian shade. Small streams with predominantly marginal emergent plants are likely to have improved retention of NH4-N as a result of shading or other means of reducing plant biomass. Streams dominated by submerged macrophytes will have impaired NH4-N retention if plant biomass is reduced because of reduced contact times between NH4-N molecules and reactive sites. In these conditions water resource managers should utilise riparian shading in concert with unshaded vegetated reaches to achieve a balance between enhanced in-stream habitat and nutrient processing capacity.     

Environmental behavior of explosives in groundwater from the Milan Army Ammunition Plant in aquatic and wetland plant treatments. Uptake and fate of TNT and RDX in plants

Uptake and fate of TNT and RDX by three aquatic and four wetland plants were studied using hydroponic, batch, incubations in explosives-contaminated groundwater amended with [U-14C]-TNT or [U-14C]-RDX in the laboratory. Substrates in which the plants were rooted were also tested. Plants and substrates were collected from a small-scale wetland constructed for explosives removal, and groundwater originated from a local aquifer at the Milan Army Ammunition Plant. This study demonstrated rapid uptake of [U-14C]-TNT derived 14C, concentration at the uptake sites and limited transport in all plants. Per unit of mass, uptake was higher in submersed than in emergent species. Biotransformation of TNT had occurred in all plant treatments after 7-day incubation in 1.6 to 3.4 mg TNT L-i, with labeled amino-dinitrotoluenes (ADNTs), three unidentified compounds unique for plants, and mostly polar products as results. Biotransformation occurred also in the substrates, yielding labeled ADNT, one unidentified compound unique for substrates, and polar products. TNT was not recovered by HPLC in plants and substrates after incubation. Uptake of [U-14C]-RDX derived 14C in plants was slower than that of TNT, transport was substantial, and concentration occurred at sites where new plant material was synthesized. As for TNT, uptake per unit of mass was higher in submersed than in emergent species. Biotransformation of RDX had occurred in all plant treatments after 13-day incubation in 1.5 mg RDX L-1, with one unidentified compound unique for plants, and mostly polar products as results. Biotransformation had occurred also in the substrates, but to a far lower extent than in plants. Substrates and plants had one unidentified 14C-RDX metabolite in common. HPLC analysis confirmed the presence of RDX in most plants and in three out of four substrates at the end of the incubation period.     

Application of plant carbon source for denitrification by constructed wetland and bioreactor: review of recent development

Water quality standard for nitrate becomes more and more strict, and the plant carbon source is widely used for denitrification by constructed wetland (CW) and bioreactor. However, the nitrate removal efficiency by different types of plant carbon source are not evaluated comprehensively. Denitrification performance of different plant carbon sources, and the influence of dosing method and pretreatment are thoroughly reviewed in this paper, which aims to investigate the accurate utilization of plant carbon source for nitrogen (as nitrate) removal. It is concluded that plant carbon source addition for all types of CWs and bioreactors can improve the nitrate removal efficiency to some extent, and the dosing method of plant carbon source for denitrification should be further studied and optimized in the future. The popular carbon sources for CW and bioreactor denitrification enhancement are woodchip, chopped macrophytes, crop plants, macrophytes litters, etc. The recommended optimum C:N ratios for CW and bioreactor are 4.0:5.0 and 1.8:3.0, respectively. The physical and biological pretreatments are selected to supply organic carbon for long-term denitrification.     

A microcosm system to evaluate the toxicity of the triazine herbicide simazine on aquatic macrophytes

This study evaluates the effects of the triazine herbicide simazine in an outdoor pond microcosm test system that contained two submerged rooted species (Myriophyllum spicatum and Elodea canadensis) and two emergent rooted species (Persicaria amphibia and Glyceria maxima) over a period of 84 days. Simazine was applied to the microcosms at nominal concentrations of 0.05, 0.5 and 5 mg/L. General biological endpoints and physiological endpoints were used to evaluate herbicide toxicity on macrophytes and the algae developing naturally in the system.Concentration-related responses of macrophytes and algae were obtained for the endpoints selected, resulting in a no observed ecologically adverse effect concentration (NOEAEC) at simazine concentrations of 0.05 mg active ingredient/L after 84 days. E. canadensis was the most negatively affected species based on length increase, which was consistently a very sensitive parameter for all macrophytes. The experimental design presented might constitute a suitable alternative to conventional laboratory single-species testing.     

Diethylaminoethyl-cellulose clean-up of a large volume naphthenic acid extract

The Athabasca oil sands of Alberta, Canada contain an estimated 174 billion barrels of bitumen. During oil sands refining processes, an extraction tailings mixture is produced that has been reported as toxic to aquatic organisms and is therefore collected in settling ponds on site. Investigation into the toxicity of these tailings pond waters has identified naphthenic acids (NAs) and their sodium salts as the major toxic components, and a multi-year study has been initiated to identify the principal toxic components within NA mixtures. Future toxicity studies require a large volume of a NA mixture, however, a well-defined bulk extraction technique is not available. This study investigated the use of a weak anion exchanger, diethylaminoethyl-cellulose (DEAE-cellulose), to remove humic-like material present after collecting the organic acid fraction of oil sands tailings pond water. The NA extraction and clean-up procedure proved to be a fast and efficient method to process large volumes of tailings pond water, providing an extraction efficiency of 41.2%. The resulting concentrated NA solution had a composition that differed somewhat from oil sands fresh tailings, with a reduction in the abundance of lower molecular weight NAs being the most significant difference. This reduction was mainly due to the initial acidification of tailings pond water. The DEAE-cellulose treatment had only a minor effect on the NA concentration, no noticeable effect on the NA fingerprint, and no significant effect on the mixture toxicity towards Vibrio fischeri.     

Case study on rehabilitation of a polluted urban water body in Yangtze River Basin

In the past three decades, the fast development of economy and urbanization has caused increasingly severe pollutions of urban water bodies in China. Consequently, eutrophication and deterioration of aquatic ecosystem, which is especially significant for aquatic vegetation, inevitably became a pervasive problem across the Yangtze River Basin. To rehabilitate the degraded urban water bodies, vegetation replanting is an important issue to improve water quality and to rehabilitate ecosystem. As a case study, a representative polluted urban river, Nanfeihe River, in Hefei City, Anhui Province, was chosen to be a rehabilitation target. In October 2009 and May 2010, 13 species of indigenous and prevalent macrophytes, including seven species emergent, one species floating leaved, and five species submersed macrophytes, were planted along the bank slopes and in the river. Through 1.5 years’ replanting practice, the water quality and biodiversity of the river had been improved. The concentrations of total nitrogen (TN), total phosphorus (TP), and ammonia nitrogen (NH₄ ⁺–N) declined by 46.0, 39.5, and 60.4 %, respectively. The species of macrophytes increased from 14 to 60, and the biodiversity of phytoplankton rose significantly in the river (p?<?0.05). The biomasses of zooplankton and benthos were also improved after the vegetation replanting. The study confirmed that vegetation replanting could alleviate the increasing water pollution and rehabilitate the degraded aquatic ecosystem. The case study would be an example for polluted urban waters restoration in the middle–downstream area of Yangtze River Base.     

Removal efficiency of a constructed wetland for wastewater treatment according to vegetation dominance

A free water surface wetland was built to treat wastewater containing metals (Cr, Ni and Zn) and nutrients from a tool factory in Santo Tomé, Santa Fe, Argentina. Eichhornia crassipes became dominant and covered about 80% of the surface throughout the first year, and decreased progressively until its disappearance. When water depth was lowered Typha domingensis steadily increased plant cover and attained 30% of the surface by the end of the study. While E. crassipes was dominant, the wetland retained 62% of the incoming Cr and 48% of the Ni. NO3- and NO2-, were also removed (65% and 78%, respectively), while dissolved inorganic phosphate (i-P(diss)) and NH4+ were not removed. Zn was below 50 microg l(-1) in both the influent and effluent. Metal concentration in the sediments did not increase and retention was mediated through macrophytes uptake. During the period of E. crassipes decline the wetland retained 49% of the incoming Cr, 45% of Ni, 58% NO3-, 94% NO2-, 58% NH4+ and 47% i-P(diss). Cr, Ni and Zn in the bottom sediment increased in the inlet but not in the outlet. Since T. domingensis became dominant, retention was 58% Cr, 48% Ni and 64% i-P(diss), while 79% NO3-, 84% NO2- and 13% NH4+ were removed. Metals in the bottom sediment increased in the inlet. In spite of the significant growth of E. crassipes at the beginning, T. domingensis remained after most of the transplanted macrophytes had disappeared. Macrophyte disappearance could be related to the overall toxicity of several environmental constrains as high pH and conductivity, metal concentration, and sulphide presence.     

Metal accumulation in aquatic macrophytes from southeast Queensland,Australia

To determine the extent of metal accumulation in some aquatic macrophytes from contaminated urban streams in southeast Queensland, plants were sampled from six sites, along with contiguous sediments. In all, 15 different species were collected, the most common genera being Typha (Cattails or Bulrushes) and Persicaria (Knotweeds). Before heavy metal analysis, plants were further separated into various morphological tissues, and five selected samples were separated into various physiological tissues. The cadmium, copper, lead and zinc content of the plants were analysed using flames AAS. In general, plant roots exhibited higher metal concentrations than the contiguous sediments. Of the metals of interest, only for zinc was there a relatively clear pattern of increasing accumulation in aquatic macrophytes with increasing sediment metal concentrations. Comparison between morphological tissues of the sampled plants found that roots consistently presented higher metal concentrations than either the stems or leaves, however unlike previous studies, this investigation revealed no consistent trend of stems accumulating more metals than the leaves. For Typha spp., metal concentrations followed the order of roots > rhizomes > leaves, while for Persicaria spp. the order was roots > leaves > stems. The submerged species Myriophyllum aquaticum accumulated the highest levels of metals overall (e.g. Zn 4300 micrograms g-1 dry weight and Cd 6.5 micrograms g-1), and the emergent macrophytes also exhibited relatively high metal contents in their roots. The leaves of the submerged and floating-leafed species collected contained relatively high quantities of the four metals of interest, compared with the leaves of emergent aquatic macrophytes. In the Typha rhizome and Persicaria stem samples analysed for internal variation in metal content, there was a pattern of increasing metal concentrations towards the external sections of the stem, both for subterranean stems (rhizomes) and above-substrate stems. For Persicaria stems, no clear pattern was observed for cadmium and lead, the two metals investigated that are not required by plants for survival.     

Application of a constructed wetland for industrial wastewater treatment: a pilot-scale study

The main objective of this study was to examine the efficacy and capacity of using constructed wetlands on industrial pollutant removal. Four parallel pilot-scale modified free water surface (FWS) constructed wetland systems [dimension for each system: 4-m (L)x1-m (W)x1-m (D)] were installed inside an industrial park for conducting the proposed treatability study. The averaged influent contains approximately 170 mg l(-1) chemical oxygen demand (COD), 80 mg l(-1) biochemical oxygen demand (BOD), 90 mg l(-1) suspend solid (SS), and 32 mg l(-1) NH(3)-N. In the plant-selection study, four different wetland plant species including floating plants [Pistia stratiotes L. (P. stratiotes) and Ipomoea aquatica (I. aquatica)] and emergent plants [Phragmites communis L. (P. communis) and Typha orientalis Presl. (T. orientalis)] were evaluated. Results show that only the emergent plant (P. communis) could survive and reproduce with a continuous feed of 0.4m(3)d(-1) of the raw wastewater. Thus, P. communis was used in the subsequent treatment study. Two different control parameters including hydraulic retention time (HRT) (3, 5, and 7d) and media [vesicles ceramic bioballs and small gravels, 1cm in diameter] were examined in the treatment study. Results indicate that the system with a 5-d HRT (feed rate of 0.4m(3)d(-1)) and vesicles ceramic bioballs as the media had the acceptable and optimal pollutant removal efficiency. If operated under conditions of the above parameters, the pilot-plant wetland system can achieve removal of 61% COD, 89% BOD, 81% SS, 35% TP, and 56% NH(3)-N. The treated wastewater meets the current industrial wastewater discharge standards in Taiwan.     

大型水生植物在水污染治理中的应用研究进展

大型水生植物在水污染治理中可以发挥多种作用。通过自身的生长代谢可以大量吸收氮、磷等水体中的营养物质 ,而其中一些种类还可以富集不同类型的重金属或吸收降解某些有机污染物 ;通过促进微生物的生长代谢 ,可以使水中大部分可生物降解有机物 (BOD)降解 ;通过抑制低等藻类的生长 ,控制富营养化的表现形式等。根据不同的生活型特点 ,利用大型水生植物进行污水处理和水体修复的方式也多种多样 ,主要包括 :以漂浮植物为主的塘系统和以挺水植物为主的人工湿地系统等。本文从生态功能发挥的角度探讨了植物对污染物降解的机理 ,并对以大型水生植物为核心的各种污水处理系统的研究进展与现状进行了综述 ,指出了利用大型水生植物进行水污染治理的研究与应用中存在的问题和发展方向     

Levels of cadmium and zinc in soil and plants following the toxic spill from a pyrite mine,Aznalcollar, Spain

On 25 April 1998, a breach of the tailings dam of the Los Frailes pyrite mine in southwestern Spain resulted in the release of 6 million m3 of acidic water and toxic sludge high in heavy metals. Contaminated material extended 40 km downstream, affecting agricultural land and parts of the wildlife-rich Do?ana Natural and National Parks, including the Entremuros, a very important area for birds. We report on the concentrations, distributions and bioavailability of zinc and cadmium in soil and vegetation from the Entremuros in November 1998 and October 1999, following 2 'cleanup' operations. Levels of Zn and Cd in soil increased significantly over this period, although this was not reflected consistently in metal concentrations in emergent macrophytes. We recommend monitoring of further cleanup attempts in order to develop means of minimizing potential impacts to wildlife in the area.