人工湿地中基质的使用现状与研究进展

分析了人工湿地中基质的作用、使用现状和存在的问题,阐述当前国内外基质研究的进展,并对基质研究的前景进行展望,提出今后研究的重点与难点.     

堵塞对复合垂直流湿地水力特征的影响

复合垂直流人工湿地系统(IVCW)堵塞后其水力特征会发生变化，通过示踪剂对小试和中试系统堵塞前后的水力特征进行了研究。结果表明，堵塞后IVCW出水流量减小，小试系统实际停留时间由堵塞前21．3h延长至32．5h，中试系统实际停留时间从19.4h延长至26．8h。IVCW堵塞后容易造成下行池表面积水，既恶化了卫生条件又降低了系统的处理能力。     

潜流人工湿地堵塞原因与对策

分析了潜流人工湿地堵塞的主要机理,详细阐述了导致其堵塞的主要影响因素,并以此为依据,从前期预防、中期减缓和后期修复等3方面提出了解决堵塞问题的有效措施,以期为今后的人工湿地设计、施工、运行和管理提供理论支持和工程借鉴。     

自然导气措施对垂直流人工湿地堵塞的影响

为解决人工湿地堵塞问题,设计了一种自然导气型垂直流人工湿地,并采用连续运行的方式,考察了水力负荷分别为0.3、0.6、0.9、1.2 m3/(m2·d)的条件下,其基质孔隙率和除污效果随时间的变化.结果表明:当在低水力负荷下运行时,自然导气对垂直流人工湿地的基质堵塞有显著的改善作用,而在较高水力负荷[1.2 m3/(m2·d)]下运行时则改善作用甚微.同时自然导气可显著提高垂直流人工湿地对污染物的去除效果,其中对氨氮去除率的提高程度大于对COD的.当水力负荷<0.9 m3/(m2·d)时,对氨氮的去除率稳定保持在较高水平,在水力负荷分别为0.3、0.6和0.9 m3/(m2·d)时,对氨氮的平均去除率分别为98.38%、89.10%、72.31%.     

人工湿地堵塞问题的探讨

近20年发展起来的人工湿地,作为一种对传统污水处理技术的廉价替代方案,越来越受到世界各国的普遍重视.通过对人工湿地运行过程中出现的填料堵塞现象进行全面分析,归纳和总结了人工湿地堵塞的影响因素,对其堵塞机理和堵塞模型进行了探讨,提出了避免堵塞的工程化解决措施和湿地堵塞后的恢复方法.     

复合垂直流人工湿地处理受污染黄河水的可行性研究

介绍了人工湿地的发展过程、定义、分类及其净化机理。详细阐述了复合垂直流人工湿地的构造、应用及净化效果。简述了人工湿地处理受污染黄河水的研究进展。介绍了复合垂直流人工湿地应用于北京奥林匹克森林公园、武汉市月湖、杭州植物园的实例,证明了复合垂直流人工湿地的优越性。最后,指出了复合垂直流人工湿地有效净化受污染黄河水的可行性。     

垂直流人工湿地用于城市污水处理厂尾水深度处理

将生态氧化池/生态砾石床组合工艺作为强化型前处理系统,与垂直流人工湿地工艺相结合,用于处理城市污水处理厂尾水,详细介绍了工艺流程和设计参数,并对主要技术经济指标进行了分析.连续5个月的试运行结果表明,整个处理系统运行稳定,对COD、BOD5、NH4+-N和TP的平均去除率分别为70.3%、69.0%、91.9%和83.1%,出水水质达到<地表水环境质量标准>(GB 3838-2002)中的Ⅲ类标准.垂直流人工湿地对主要污染物的平均去除率均在55%以上.     

利用复合垂直流人工湿地处理生活污水

采用复合垂直流人工湿地处理了城镇居民生活污水，结果表明，该新型人工湿地对城市生活污水具有良好的净化作用，对NH3-N、TP、COD、BOD5、TSS、细菌总数和浊度的去除率高达80％以上，出水水质达到了国家杂用水标准。     

垂直流人工湿地处理生活污水的影响因素分析

选用鸢尾、酸模、兰草、葱兰这4种陆生植物构建垂直流人工湿地并处理生活污水,考察了水力停留时间、水力负荷、温度以及湿地植物种类对处理效果的影响.结果表明:在较长水力停留时间(24 h左右)、较低水力负荷(0.3 m/d)条件下,湿地系统对污染物的去除率较高;随着温度的升高,湿地系统的除污效果提高;湿地中植物的长势好于自然环境中的,其中酸模的净化能力最强,其生长成熟时对氨氮、总磷的去除率稳定在95%左右,对COD的去除率在60%左右.     

强化型垂直流人工湿地用于污水处理厂尾水深度处理

以生态氧化池作为垂直流人工湿地的强化前处理工艺,将组合工艺应用于污水处理厂尾水深度处理,简要介绍了工艺流程和设计参数,并对稳定期的运行结果进行了分析和讨论.连续12个月的水质监测数据表明,深度处理系统运行稳定,对COD、BOD5 、NH4+-N和TP的平均去除率分别为61.8％、64.4％、82.6％、75.2％,出水水质优于《地表水环境质量标准》(GB 3838-2002)的Ⅳ类标准.生态氧化池和垂直流人工湿地对主要污染物的去除特征存在显著差异,其中垂直流人工湿地对上述污染物的平均去除率为50％～80％.     

Bacterial carbon utilization in vertical subsurface flow constructed wetlands

Subsurface vertical flow constructed wetlands with intermittent loading are considered as state of the art and can comply with stringent effluent requirements. It is usually assumed that microbial activity in the filter body of constructed wetlands, responsible for the removal of carbon and nitrogen, relies mainly on bacterially mediated transformations. However, little quantitative information is available on the distribution of bacterial biomass and production in the "black-box" constructed wetland. The spatial distribution of bacterial carbon utilization, based on bacterial (14)C-leucine incorporation measurements, was investigated for the filter body of planted and unplanted indoor pilot-scale constructed wetlands, as well as for a planted outdoor constructed wetland. A simple mass-balance approach was applied to explain the bacterially catalysed organic matter degradation in this system by comparing estimated bacterial carbon utilization rates with simultaneously measured carbon reduction values. The pilot-scale constructed wetlands proved to be a suitable model system for investigating microbial carbon utilization in constructed wetlands. Under an ideal operating mode, the bulk of bacterial productivity occurred within the first 10cm of the filter body. Plants seemed to have no significant influence on productivity and biomass of bacteria, as well as on wastewater total organic carbon removal.     

Mathematical model for analysis of recirculating vertical flow constructed wetlands

The recirculating vertical flow constructed wetland (RVFCW) was developed for the treatment of domestic wastewater (DWW). In this system, DWW is applied to a vertical flow bed through which it trickles into a reservoir located beneath the bed. It is then recirculated back to the root zone of the bed. In this study, a compartmental model was developed to simulate the RVFCW. The model, which addresses transport and removal kinetics of total suspended solids, 5-day biological oxygen demand and nitrogen, was fitted to kinetical results obtained from pilot field setups and a local sensitivity analysis was performed on the model parameters and operational conditions. This analysis showed that after 5 h of treatment water quality is affected more by stochastic events than by the model parameter values, emphasizing the stability of the RVFCW system to large variations in operational conditions. Effluent quality after 1 h of treatment, when the sensitivity analysis showed the parameter impacts to be largest, was compared to model predictions. The removal rate was found to be dependent on the recirculation rate. The predictions correlated well with experimental observations, leading to the conclusion that the proposed model is a satisfactory tool for studying RVFCWs.     

折流式人工湿地处理雨水径流的机理初步分析

针对目前人工湿地存在的问题,设计了一套新型人工湿地——折流式人工湿地床与氧化塘组合,目的是将其用于雨水的处理应用上,通过试验证明其用于处理雨水时具有良好的处理效果且运行效果稳定。     

Comparison of phosphorus removal between vertical subsurface flow constructed wetlands with different substrates

Phosphorus removal by constructed wetlands is a key strategy in diffuse pollution control. Phosphorus retention by experimental unplanted vertical-flow constructed wetlands depends on substrate, influent quality and hydraulic residence time (HRT). The maximal phosphorus adsorption capacities of shale, gravel, ironstone and hornblende were 619.7, 89.05, 324.9 and 153.1 mg/kg, respectively, when the grain size ranged between 0.5 and 1.0 mm. Phosphorus adsorption capacities of shale, ironstone and hornblende were best explained by Langmuir adsorption isotherms. In comparison, Freundlich adsorption isotherms fitted gravel well. In separate column experiments with eutrophic Jin River water, shale showed better soluble reactive phosphorus (SRP) and total phosphorus (TP) retention performances than gravel, ironstone and hornblende. When the HRT was 2.2 days, the mean SRP removal rates were 96.7, 21.1, 33.6 and 33.0% for shale, gravel, ironstone and hornblende, respectively. Findings indicate that both SRP and TP removal rates increased when the HRT was prolonged.     

Life cycle assessment of vertical and horizontal flow constructed wetlands for wastewater treatment considering nitrogen and carbon greenhouse gas emissions

Life cycle assessment (LCA) is used to compare the environmental impacts of vertical flow constructed wetlands (VFCW) and horizontal flow constructed wetlands (HFCW). The LCAs include greenhouse gas (N₂O, CO₂ and CH₄) emissions. Baseline constructed wetland designs are compared to different treatment performance scenarios and to conventional wastewater treatment at the materials acquisition, assembly and operation life stages. The LCAs suggest that constructed wetlands have less environmental impact, in terms of resource consumption and greenhouse gas emissions. The VFCW is a less impactful configuration for removing total nitrogen from domestic wastewater. Both wetland designs have negligible impacts on respiratory organics, radiation and ozone. Gaseous emissions, often not included in wastewater LCAs because of lack of data or lack of agreement on impacts, have the largest impact on climate change. Nitrous oxide accounts for the increase in impact on respiratory inorganic, and the combined acidification/eutrophication category. The LCAs were used to assess the importance of nitrogen removal and recycling, and the potential for optimizing nitrogen removal in constructed wetlands.     

Hydraulics and flow modelling of water treatment wetlands constructed on peatlands in Northern Finland

In this study, we evaluated flow structure, effective flow area (A(eff)) and effective porosity (theta(eff)) in three peatlands using the stable isotope (18)O/(16)O ratio and tracer tests. We also applied the readily available groundwater modelling MODFLOW code for wetland flow modelling and simulated in one study site how the hydraulic performance of the wetland will be improved by changing the design of the distribution ditch. Preferential flow paths occurred in all three studied wetlands and A(eff) varied from 40% to 90% of total wetland area while theta(eff) was 0.75-0.99. Constructed flow models accurately simulated the hydraulic head across wetlands (r(2)=0.95-0.99). Similarities between the flow models and the stable isotope distributions observed in this study suggest possibilities in using MODFLOW to design peatlands. The improvement of the inlet ditch configuration (ditch length/wetland width>0.45) can prevent or reduce short-circuiting and dead zones in peatlands treating wastewater.     

Model-based design of horizontal subsurface flow constructed treatment wetlands: a review

The increasing application of constructed wetlands for wastewater treatment coupled with increasingly strict water quality standards is an ever growing incentive for the development of better process design tools. This paper reviews design models for horizontal subsurface flow constructed treatment wetlands, ranging from simple rules of thumb and regression equations, to the well-known first-order k-C* models, Monod-type equations and more complex dynamic, compartmental models. Especially highlighted in this review are the model constraints and parameter uncertainty. A case study has been used to demonstrate the model output variability and to unravel whether or not more complex but also less manageable models offer a significant advantage to the designer.     

Effect of reeds and feeding operations on hydraulic behaviour of vertical flow constructed wetlands under hydraulic overloads

Vertical flow constructed wetlands (VFCWs) have been very successful in France over the last 5 years. The sizing of VFCWs is still roughly based on organic load acceptance with slight clear water intrusion into the sewerage system which is often wrong in the context of small communities. To specify the hydraulic limits would be of great help to Water Authorities in deciding at what point is it preferable to build separate sewers rather than adapt the wastewater treatment plant. The study of the hydraulic limits of reed beds, based on the knowledge of hydrodynamics in unsaturated porous media, shows the ability of the system to accept flow overloads. Measuring different parameters (flow, pollutant removal, infiltration rate (IR), pressure head profiles) in pilot and full-scale studies, we explain the hydraulic behaviour of the filter, and the role of reeds and batch frequency on the IRs. Consequently, new hydraulic limits with accompanying sizing rules and operational recommendations according to the level of deposit on the filter surface are suggested. The study shows the robustness of reed beds systems as designed in France to accept hydraulic overloads. Overloads up to ten times the dry weather flow are possible whilst still complying with the European standards.     

Simulation of the treatment performance of outdoor subsurface flow constructed wetlands in temperate climates

Numerical models are a means to increase the understanding of the processes occurring in the "black box" constructed wetland. Once reliable models for constructed wetlands are available they can be also used for evaluating and improving existing design criteria. The paper shows simulation results for outdoor experimental subsurface vertical flow constructed wetlands using CW2D, a multi-component reactive transport module developed to simulate transport and reactions of the organic matter, nitrogen and phosphorus in subsurface flow constructed wetlands. The surface area of the experimental vertical flow bed was 20 m(2). The organic load applied was 27 g COD m(-2) d(-1) (corresponding to a specific surface area of 3 m(2) per person). The aim of the work is to calibrate the model for temperature dependency that has been implemented in CW2D. Water temperature during the investigation period varied between 4 degrees C and 18 degrees C. The measured effluent concentrations during summer could be simulated using the standard CW2D parameter set when the flow model was calibrated well. However, the increasing effluent concentrations at low temperatures could not be simulated with the standard CW2D parameter set where temperature dependencies are considered only for maximum growth, decay, and hydrolysis rates. By introducing temperature dependencies for half-saturation constants for the hydrolysis and nitrification processes it was possible to simulate the observed behaviour. The work presented is a step on the way to validate the CW2D module. Model validation is a necessary step before numerical simulation can be finally used in practice, e.g. for checking existing design guidelines.