不同布水方式下水平潜流人工湿地水动力学机制研究

通过6种布水方式（一般推流、多向入流、部分回流、波流、对角流、多点进水）下水平潜流人工湿地的脉冲示踪剂实验研究，获得其水力停留时间概率分布密度曲线。用4种不同概率分布函数（正态分布、对数正态分布、卡方分布、瑞利分布）对其水力停留时间的概率分布密度进行拟合分析，结果表明：对数正态分布的拟合效果更好。将对流扩散模型和连续反应器模型分别用于6种布水方式下的示踪剂迁移过程模拟，结果表明：连续反应器模型比较适合模拟部分回流式布水方式，对流扩散模型能够较好模拟其他5种布水方式。考虑多向入流和多点进水的示踪剂浓度叠加作用，进一步利用基于对流扩散机制的叠加模型进行示踪剂迁移过程模拟，结果表明：基于对流扩散机制的叠加模型能够较好模拟多向入流、多点进水类型的水平潜流人工湿地。     

不同布水方式下水平潜流人工湿地水动力学机制研究

通过6种布水方式(一般推流、多向入流、部分回流、波流、对角流、多点进水),进行了水平潜流人工湿地的脉冲示踪剂试验研究,获得其水力停留时间概率分布密度曲线。分别用4种不同概率分布函数(正态分布、对数正态分布、卡方分布、瑞利分布)对其水力停留时间的概率分布密度进行拟合分析,结果表明:对数正态分布的拟合效果最好。将对流扩散模型和连续反应器模型用于示踪剂的迁移过程模拟,结果表明:连续反应器模型比较适合模拟部分回流式布水方式,对流扩散模型则能够较好模拟其他5种布水方式。考虑多向入流和多点进水的示踪剂浓度叠加作用,进一步利用基于对流扩散机制的叠加模型进行示踪剂迁移过程模拟,结果表明:基于对流扩散机制的叠加模型能够较好模拟多向入流、多点进水类型的水平潜流人工湿地。     

水平潜流人工湿地脱氮除磷研究进展

总结了水平潜流人工湿地的脱氮除磷机理,分析了进水水质、植物、基质、温度和水力停留时间这5种影响处理效果的主要因素,从不同角度论述了提高脱氮除磷效果所采取的措施,并探讨了水平潜流人工湿地存在的局限性和发展趋势。     

Optimization of subsurface vertical flow constructed wetlands for wastewater treatment.

Constructed wetlands (CWs) use the same processes that occur in natural wetlands to improve water quality and are used worldwide to treat different qualities of water. This paper shows the results of an Austrian research project having the main goals to optimize vertical flow beds in terms of surface area requirement and nutrient removal, respectively. It could be shown that a subsurface vertical flow constructed wetland (SSVFCW) operated with an organic load of 20 g COD x m(-2) x d(-1) (corresponding to a specific surface area demand of 4 m2 per person) can fulfil the requirements of the Austrian standard regarding effluent concentrations and removal efficiencies. During the warmer months (May - October), when the temperature of the effluent is higher than 12 degrees C, the specific surface area might be further reduced. Even 2 m2 per person have been proven to be adequate. Enhanced nitrogen removal of 58% could be achieved with a two-stage system (first stage: grain size for main layer 1-4 mm, saturated drainage layer; and second stage: grain size for main layer 0.06-4 mm, free drainage) that was operated with an organic load of 80 g COD x m(-2) x d(-1) for the first stage (1 m2 per person), i.e. 40 g COD x m(-2) x d(-1) for the two-stage system (2 m2 per person). Although the two-stage system was operated with higher organic loads a higher effluent quality compared to a single-stage SSVFCW (grain size for main layer 0.06-4 mm, free drainage, organic load 20 g COD x m(-2) x d(-1)) could be reached.     

Effect of diffusional mass transfer on the performance of horizontal subsurface flow constructed wetlands in tropical climate conditions

The effect of mass transfer on the removal rate constants of BOD5, NH3, NO3 and TKN has been investigated in a Horizontal Subsurface Flow Constructed Wetland (HSSFCW) planted with Phragmites mauritianus. The plug flow model was assumed and the inlet and outlet concentrations were used to determine the observed removal rate constants. Mass transfer effects were studied by assessing the influence of interstitial velocity on pollutant removal rates in CW cells of different widths. The flow velocities varied between 3-46 m/d. Results indicate that the observed removal rate constants are highly influenced by the flow velocity. Correlation of dimensionless groups namely Reynolds Number (Re), Sherwood Number (Sh) and Schmidt Number (Sc) were applied and log-log plots of rate constants against velocity yielded straight lines with values beta = 0.87 for BOD5, 1.88 for NH3, 1.20 for NO3 and 0.94 for TKN. The correlation matched the expected for packed beds although the constant beta was higher than expected for low Reynolds numbers. These results indicate that the design values of rate constants used to size wetlands are influenced by flow velocity. This paper suggests the incorporation of mass transfer into CW design procedures in order to improve the performance of CW systems and reduce land requirements.     

Removal efficiency of subsurface vertical flow constructed wetlands for different organic loads.

Using subsurface vertical flow constructed wetlands (SSVFCWs) with intermittent loading it is possible to fulfil the stringent Austrian effluent standards regarding nitrification. For small plants (less than 500 persons) standards for ammonia nitrogen concentration have to be met at water temperatures higher than 12 degrees C, effluent concentrations and treatment efficiencies for organic matter have to be met the whole year around. According to the Austrian design standards the required surface area for SSVFCWs treating wastewater was 5 m2 per person. Within the first part of an Austrian research project the goal was to optimise, i.e. minimise the surface area requirement of vertical flow beds. Therefore, three SSVFCWs with a surface area of 20 m2 each have been operated in parallel. The organic loads applied were 20, 27 and 40 g COD/m2/d, which corresponds to a specific surface area requirement of 4, 3 and 2 m2 per PE, respectively. The paper compares the effluent concentrations and elimination efficiencies of the three parallel operated beds. It could be shown that a specific area demand of 4 m2 per person is suitable to be included in the revision of the Austrian design standard. Additionally it could be shown that during the warmer seasons (May-October) when the temperature of the effluent is higher than 12 degrees C the specific surface area might be further reduced; even 2 m2 per person has been proven to be adequate.     

Application of culture-independent methods to assess the bacteria removal efficiency of subsurface flow constructed wetlands.

The bacteriologic treatment efficiency of vertical and horizontal subsurface flow constructed wetlands (SFCWs) was analysed in two multistage wastewater treatment systems by culture dependent and independent methods. When assessed with standard cultivation procedures, bacteria removal efficiency of the vertical and horizontal SFCWs was similar. However, microscopic enumerations of the wastewater bacteria after DNA staining revealed a completely different removal pattern: bacteria removal efficiency of the horizontal SFCWs was in general low and erratic, whereas the vertical SFCWs displayed high bacteria removal rates. The discrepancies in the results obtained by bacteria enumeration and cultivation was due to a strong decrease in bacterial culturability after treatment by the horizontal SFCWs, leading to overestimation of the real bacterial concentrations in these effluents. Additionally, a PCR based approach for the detection of the enteropathogenic bacteria Campylobacter jejuni and Yersinia enterocolitica was tested in the wastewater samples. The methods were specific and reproducible in the analysed samples and could be carried out within 12 h, proving very adequate as an alternative to cultivation. This work recommends a review of the current standard methodology for wastewater quality surveillance, as well as of the design of SFCW.     

Comparison of measured and simulated distribution of microbial biomass in subsurface vertical flow constructed wetlands.

The multi-component reactive transport module CW2D has been developed to model transport and reactions of the main constituents of municipal wastewater in subsurface flow constructed wetlands and is able to describe the biochemical elimination and transformation processes for organic matter, nitrogen and phosphorus. It has been shown that simulation results match the measured data when the flow model can be calibrated well. However, there is a need to develop experimental techniques for the measurement of CW2D model parameters to increase the quality of the simulation results. Over the last years methods to characterise the microbial biocoenosis in vertical subsurface flow constructed wetlands have been developed. The paper shows measured data for microbial biomass and their comparison with simulation results using different heterotrophic lysis rate constants.     

Model experiments on improving nitrogen removal in laboratory scale subsurface constructed wetlands by enhancing the anaerobic ammonia oxidation.

Anaerobic ammonia oxidation (Anammox) has been identified as a new general process-strategy for nitrogen removal in wastewater treatment. In order to evaluate the role and effects of the Anammox process in wetlands, laboratory-scale model experiments were performed with planted fixed bed reactors. A reactor (planted with Juncus effusus) was fed with synthetic wastewater containing 150-200 mg L(-1) NH4+ and 75-480 mg L(-1) NO2(-). Under these operating conditions, the plants were affected by the high ammonia and nitrite concentrations and the nitrogen removal rate fell within the same range of 45-49 mg N d(-1) (equivalent to 0.64-0.70 g Nm(-2)d(-1)) as already reported by other authors. In order to stimulate the rate of nitrogen conversion, the planted reactor was inoculated with Anammox biomass. As a result, the rate of nitrogen removal was increased 4-5-fold and the toxic effects on the plants also disappeared. The results show that, in principle, subsurface flow wetlands can also function as an "Anammox bioreactor". However, the design of a complete process for the treatment of waters with a high ammonia load and, in particular, the realisation of simple technical solutions for partial nitrification have still to be developed.     

Modelling and evaluation of nitrogen removal performance in subsurface flow and free water surface constructed wetlands.

With the aim of protecting drinking water sources in rural regions, pilot-scale subsurface water flow (SSF) and free water surface flow (FWS) constructed wetland systems were evaluated for removal efficiencies of nitrogenous pollutants in tertiary stage treated wastewaters (effluent from the Pasak?y biological nutrient removal plant). Five different hydraulic application rates and emergent (Canna, Cyperus, Typhia sp., Phragmites sp., Juncus, Poaceae, Paspalum and Iris) and floating (Pistia, Salvina and Lemna) plant species were assayed. The average annual NH4-N, NO3-N and organic-N treatment efficiencies were 81, 40 and 74% in SSFs and 76, 59 and 75% in FWSs, respectively. Two types of the models (first-order plug flow and multiple regression) were tried to estimate the system performances. Nitrification, denitrification and ammonification rate constants (k20) values in SSF and FWS systems were 0.898 d-1 and 0.541 d(-1), 0.486 d(-1) and 0.502 d(-1), 0.986 d(-1) and 0.908, respectively. Results show that the first-order plug flow model clearly estimates slightly higher or lower values than observed when compared with the other model.     

Nitrogen elimination from landfill leachates using an extra carbon source in subsurface flow constructed wetlands.

A three-stage constructed wetland for leachate treatment was monitored on a landfill at a pilot scale. The plant had been designed to achieve at least 75% nitrogen removal. NH4-N input concentration was 240 (median) up to 290 mgl(-1) and COD concentration was 455 to 511 mgl(-1), respectively. A 14 m2 vertical flow sand filter plus a 14 m2 horizontal flow sand filter followed by a 3.3 m2 vertical flow sand filter was chosen. Acetic acid was added to the horizontal flow system for denitrification. The results showed a very stable nitrification rate within the vertical flow system of 94% (median) at NH4-N loading rates of about 10 (median) up to 17 gm(-2)d(-1). Denitrification was mainly dependent on the dosing of acetic acid and could reach a maximum of 98%. One interesting effect was the production of nitrite in the horizontal flow sand filter. This could efficiently be eliminated by the subsequent vertical flow sand filter. The chosen concept proved to be very effective for nitrogen removal. In combination with a final activated carbon filter the COD effluent concentrations could be easily and safely controlled. The design of denitrification reed beds showed a further potential for optimization.     

The role of plant uptake on the removal of organic matter and nutrients in subsurface flow constructed wetlands: a simulation study.

Plants in constructed wetlands have several functions related to the treatment processes. It is generally agreed that nutrient uptake is a minor factor in constructed wetlands treating wastewater compared to the loadings applied. For low loaded systems plant uptake can contribute a significant amount to nutrient removal. The contribution of plant uptake is simulated for different qualities of water to be treated using the multi-component reactive transport module CW2D. CW2D is able to describe the biochemical elimination and transformation processes for organic matter, nitrogen and phosphorus in subsurface flow constructed wetlands. The model for plant uptake implemented describes nutrient uptake coupled to water uptake. Literature values are used to calculate potential water and nutrient uptake rates. For a constructed wetland treating municipal wastewater a potential nutrient uptake of about 1.9% of the influent nitrogen and phosphorus load can be expected. For lower loaded systems the potential uptake is significantly higher, e.g. 46% of the nitrogen load for treatment of greywater. The potential uptake rates could only be simulated for high loaded systems i.e. constructed wetlands treating wastewater. For low loaded systems the nutrient concentrations in the liquid phase were too low to simulate the potential uptake rates using the implemented model for plant uptake.     

Development of a horizontal subsurface flow modular constructed wetland for urban runoff treatment

Constructed wetlands (CWs) are well recognized as having low construction and maintenance cost and low energy requirement. However, CW design has been mainly based on rule-of-thumb approaches. In this study, the efficiency of a modular horizontal subsurface flow (HSSF) CW using four different design schemes was investigated. Based on the results, the four systems have attained more than 90% removal of total suspended solids and more than 50% removal efficiency for total phosphorus, PO(4)-P and Zn. The planted system achieved higher pollutant removal rates than the unplanted system. In terms of media, bottom ash was more effective than woodchip in reducing the pollutants. Considering the flow length, optimum removal efficiency was achieved after passing the sedimentation tank and vertical media layer; with respect to depth, more pollutants were removed in the upper sand layer than in the lower gravel layer. This study recommended a surface area of 0.25 to 0.8% of catchment area for planted CW and 0.26 to 0.9% for unplanted CW using the 7.5 to 10 mm design rainfall.     

Mechanical resistance properties of gravel used in subsurface flow constructed wetlands: implications for clogging

Gravel constitutes the filter medium in subsurface flow constructed wetlands (SSF CWs) and its porosity and hydraulic conductivity decrease over time (clogging), limiting the lifespan of the systems. Using gravel of poor quality accelerates clogging in wetlands. In this study, gravel samples from six different wetland systems were compared with regards to their mineral composition and mechanical resistance properties. Results showed that both mineralogy and texture are related to mechanical resistance. Accordingly, gravel with high content of quartz (> 80%) showed a lower percentage of broken particles (0.18-1.03%) than those with lower content of quartz (2.42-4.56% media broken). Although granite is formed by high durability minerals, its non-uniform texture results in a lower resistance to abrasion (ca. 10% less resistance than calcareous gravel). Therefore, it is recommended to use gravels composed mainly of quartz or, when it is not available, limestone gravels (rounded and uniform) are recommended instead. The resistance to abrasion (LAA test) seems to be a good indicator to determine the mechanical properties of gravels used in CWs. It is recommended to use gravels with LAA below 30% in order to avoid a rapid clogging due to gravel crumbling and subsequent mineral solids accumulation.     

Damk?hler number design method to avoid clogging of subsurface flow constructed wetlands by heterotrophic biofilms.

Clogging of subsurface flow (SSF) treatment wetlands from excess biofilm growth is a design problem for which only empirical guidelines exist. A method is proposed to systematically analyse this type of clogging as a design tool. In recognition of the physical reality that most SSF treatment wetland processes are a function of biofilm surface area, a Damk?hler number (Da) definition based on aggregate specific surface area is used to investigate a method of predicting clogging induced by heterotrophic biofilms growing on treatment media.     

三段式水平潜流人工湿地的中试研究

采用三段式水平潜流人工湿地处理生活污水,具有较强的抗污染负荷冲击能力,出水水质可达GB 18918—2002一级A标准。人工湿地对COD_(Cr)的去除规律符合一级反应,COD_(Cr)与长度的关系为C_i-C_*=90.356L~(-0.5201)。     

Enhancing the removal of arsenic, boron and heavy metals in subsurface flow constructed wetlands using different supporting media

The presence of arsenic and heavy metals in drinking water sources poses a serious health risk due to chronic toxicological effects. Constructed wetlands have the potential to remove arsenic and heavy metals, but little is known about pollutant removal efficiency and reliability of wetlands for this task. This lab-scale study investigated the use of vertical subsurface flow constructed wetlands for removing arsenic, boron, copper, zinc, iron and manganese from synthetic wastewater. Gravel, limestone, zeolite and cocopeat were employed as wetland media. Conventional gravel media only showed limited capability in removing arsenic, iron, copper and zinc; and it showed virtually no capability in removing manganese and boron. In contrast, alternative wetland media: cocopeat, zeolite and limestone, demonstrated significant efficiencies--in terms of percentage removal and mass rate per m3 of wetland volume--for removing arsenic, iron, manganese, copper and zinc; their ability to remove boron, in terms of mass removal rate, was also higher than that of the gravel media. The overall results demonstrated the potential of using vertical flow wetlands to remove arsenic and metals from contaminated water, having cocopeat, zeolite or limestone as supporting media.     

水平潜流湿地对城市湖泊冬季净化效果的分析

以西安市兴庆湖为研究对象,实验研究冬季水平潜流人工湿地对城市湖泊水体的净化效果。实验参照排入西安市兴庆湖的混合污水水质,测定了化学需氧量、总氮、总磷、氨氮的去除率,并分析了季节变化对净化效果的影响。为提高后续湿地处理系统正常运行的可靠性,提出人工湿地在低温环境运行条件下的措施。     

Simulation of a subsurface vertical flow constructed wetland for CSO treatment.

Constructed wetlands (CWs) have proved to be a highly effective measure to reduce the ecological impact of combined sewer overflows (CSOs) on receiving waters. Due to the stochastic nature of the loading regime and the multitude of environmental influences, assessment of the performance of such plants requires detailed mathematical modelling. A multi-component reactive transport module (CW2D) was applied to simulate the flow, transport and degradation processes occurring in a CW for CSO treatment. CW2D was originally developed to simulate the treatment of municipal wastewater in subsurface flow CWs. Loading and operational conditions in CSO treatment differ fundamentally from the conditions occurring for wastewater treatment. Despite these differences, first results from the simulation of lab-scale experiments show, that the model is generally applicable to this type of plant. Modelling of adsorption, degradation processes, and influent fractionation, however, require further research.     

北方潜流人工湿地植物布局与管理探讨

<正>官厅水库黑土洼人工湿地示范工程建于2003年,由永定河引水工程、稳定塘、人工湿地、退水渠等部分组成,工程充分利用黑土洼村附近的有利地形,运用生态工程原理,采用无污染、效率高的人工湿地技术来处