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.     

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)。     

A two-stage subsurface vertical flow constructed wetland for high-rate nitrogen removal.

By using a two-stage constructed wetland (CW) system operated with an organic load of 40 gCOD.m(-2).d(-1) (2 m2 per person equivalent) average nitrogen removal efficiencies of about 50% and average nitrogen elimination rates of 980 g N.m(-2).yr(-1) could be achieved. Two vertical flow beds with intermittent loading have been operated in series. The first stage uses sand with a grain size of 2-3.2 mm for the main layer and has a drainage layer that is impounded; the second stage sand with a grain size of 0.06-4 mm and a drainage layer with free drainage. The high nitrogen removal can be achieved without recirculation thus it is possible to operate the two-stage CW system without energy input. The paper shows performance data for the two-stage CW system regarding removal of organic matter and nitrogen for the two year operating period of the system. Additionally, its efficiency is compared with the efficiency of a single-stage vertical flow CW system designed and operated according to the Austrian design standards with 4 m2 per person equivalent. The comparison shows that a higher effluent quality could be reached with the two-stage system although the two-stage CW system is operated with the double organic load or half the specific surface area requirement, respectively. Another advantage is that the specific investment costs of the two-stage CW system amount to 1,200 EUR per person (without mechanical pre-treatment) and are only about 60% of the specific investment costs of the singe-stage CW system.     

System design and treatment efficiency of a surface flow constructed wetland receiving runoff impacted stream water

This study reported the efficiency of a free water surface flow constructed wetland (CW) system that receives runoff impacted stream water from a forested and agricultural watershed. Investigations were conducted to examine the potential effect of hydraulic fluctuations on the CW as a result of storm events and the changes in water quality along the flow path of the CW. Based on the results, the incoming pollutant concentrations were increased during storm events and greater at the near end of the storm than at the initial time of storm. A similar trend was observed to the concentrations exiting the CW due to the wetland being a relatively small percentage of the watershed (<0.1%) that allowed delays in runoff time during storm events. The concentrations of most pollutants were significantly reduced (p < 0.05) except for nitrate (p = 0.5). Overall, this study suggests that the design of the system could feasibly function for the retention of most pollutants during storm events as the actual water quality of the outflow was significantly better by 21-71% than the inflow and the levels of pollutants were reduced to appreciable levels.     

Landfill leachate treatment by an experimental subsurface flow constructed wetland in tropical climate countries.

Municipal leachate was treated in an experimental unit of constructed wetlands of subsurface flow type. The parameters studied were organics (BOD and COD), solids and heavy metals (Zn, Ni, Cu, Cr and Pb). Using two types of emergent plants of Scirpus globulosus and Eriocaulon sexangulare, more than 80% removal was achieved for all the parameters. E. sexangulare removed organics and heavy metals better than Scirpus globulosus. A higher concentration of heavy metals in the influent did not change the removal efficiency.     

Vertical flow constructed wetland for textile effluent treatment.

A pulse feed vertical flow constructed wetland (VFCW) proved to be efficient in the treatment of a textile effluent being able to buffer, dilute and treat an Acid Orange (AO7) accidental discharge. The influence of the flooding level (FL) and pulse feed (PF) duration on the removal efficiencies of a VFCW was examined. Average AO7 removal efficiencies of 70% were achieved for an AO7 Inlet concentration of 700 mgl(-1) applied during 15 min cycle(-1) (every three hours) at a hydraulic load of 13 lm(-2) cycle(-1) and an FL of 21%. The VFCW was modelled by analogy with a combination of ideal reactors. The simplest combination that best reproduced the experimental results was an association of 2 reactors in series plus 1 reactor accounting the dead volumes. The model parameters helped to understand the hydrological and kinetic processes occurring in VFCW. Through the model simulation it was shown that 3 VFCW in series were enough to efficiently treat an organic mass load of 76 gAO7 m(-2) day(-1) in 9 hours and fulfil the discharge legislation. In this work it was possible to establish that the overall degradation kinetics was of first order.     

Use of headspace solid-phase microextraction to characterize odour compounds in subsurface flow constructed wetland for wastewater treatment.

A headspace solid-phase microextraction (HS-SPME) preconcentration method was applied to the analysis of some of the major odorous compounds occurring in wastewater using GC/MS or GC/NPD detection. The detection limit for volatile amines, volatile fatty acids, and volatile alkylsulphides ranged from 3 to 100, 2 to 150, and 0.0006 to 0.035 microg/L, respectively. The SPME method was used to examine the fate of odorous compounds in the subsurface flow constructed wetlands (SFCW) operated under different hydraulic loading rate (HLR), bed aspect ratio, and granular medium size. Among the experimental conditions evaluated in the SFCW beds, HLR was found to be the most important factor influencing the evolution of the studied compounds. There were also significant differences among bed types in the behaviour of ammonia (NH3), acetic acid (Ac), isovaleric acid (IsoA), propionic acid (PrA), and dimethylsulphide. Aspect ratio and medium granular size were minor factors influencing SFCW performance. The major odour compounds by mass in the effluent of SFCW with different operational conditions were NH3 and Ac. Further removal of these two compounds is considered as very important from the viewpoint of chemical composition. On the other hand, Relative Odour Intensity (ROI: ratio between the absolute concentration to the odour threshold concentration) suggested that PrA and IsoA were the two major compounds responsible for odour intensity. Thus, further removal of these two compounds is viewed as very important for the effluent deodorization, especially for PrA. From our results, this compound appears to be produced by processes occurring in the SFCW.     

Total and hexavalent chromium removal in a subsurface horizontal flow (h-SSF) constructed wetland operating as post-treatment of textile wastewater for water reuse

In this study we investigated total and hexavalent chromium removal in an h-SSF constructed wetland (CW) planted with Phragmites australis and operating as post-treatment of effluent wastewater from an activated sludge plant serving the textile industrial district of Prato (Italy). Two measurement campaigns were carried out in 2006 and 2008-2010 in which more than 950 inlet and outlet samples were analyzed. When inlet and outlet concentrations were compared one to the other, the latter were found to be significantly lower than the former (p < 0.001); during the entire period of investigation, removal of hexavalent chromium equal to about 70% was achieved. Outlet concentrations ranged between values lower than the quantification limit (0.5 microg L(-1)) and 4.5 microg L(-1), and in all cases were therefore lower than the limit indicated for hexavalent chromium in the Italian regulation for water reuse (5 microg L(-1)). The comparison of the removal efficiencies achieved for hexavalent and trivalent chromium during the two campaigns suggested that the removal of the former can be sustained in the long term, while for the latter, the treatment efficiency is more sensitive to the age of the CW, being that it is it based on trivalent chromium retention in the reed bed.     

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.     

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     

The effect of the scale of horizontal subsurface flow constructed wetlands on flow and transport parameters.

Horizontal subsurface flow constructed wetlands have proven their efficiency in treating wastewater and removing the pollutants of concern. Treatment efficiency depends on the wastewater residence time, which is a function of the hydraulic loading and the physical conditions of the constructed filter system, which can be described with effective parameters such as: hydraulic conductivity, porosity, dispersivity etc. Because spatial variability is often scale dependent, these effective parameters may be affected by the scale of the system being studied. In this paper the results of tracer experiments in constructed filters using saturated horizontal flow at three scales (small and medium lab scales and full-scale system) using the same filter media is reported. Light-weight aggregate (filter media termed Filtralite-P) was used at all scales. Increasing the scale was associated with increasing dispersivity, meanwhile hydraulic conductivity experienced dramatic reduction and variation by increasing the examined scale. Observed changes in the hydraulic parameters indicate that heterogeneity at different scales should be taken into account when the performance of LWA filters are evaluated from small-scale experiments.     

上下回流人工湿地预处理微污染水库水的研究

采用上下回流潜流人工湿地对微污染水库水进行预处理试验。根据试验数据,构建了上下回流潜流人工湿地系统CODCr、TN、TP的一级动力学模拟方程。结果表明:在水力负荷为0.4m3/(m2.d)条件下,CODCr、TN、NH3-N、TP的平均去除率均分别达到56.06%、58.97%、55.91%和50.56%。湿地系统夏季处理效果明显好于其他季节。使用周期按20年考虑,日均进水量3.6m3/d,湿地建设成本为2100元,水的处理成本为0.13元/m3,这表明采用人工湿地预处理微污染水库水是经济可行的。     

Effect of dosing regime on nitrification in a subsurface vertical flow treatment wetland system

In this study, the effect of dosing regime on nitrification in a subsurface vertical flow treatment wetland system was investigated. The experimental unit was composed of four circular concrete tanks (1 m diameter and 80 cm deep), filled with gravel (1-2 cm) and planted with Cyperus alternifolius L. Synthetic wastewater with average chemical oxygen demand (COD) and ammonia nitrogen of 1,151 and 339 mg/L was fed into each tank. Different feeding and resting periods were applied: continuous flow (tank 1), 4 hrs on and 4 hrs off (tank 2), 1 hr on and 3 hrs off (tank 3) and 15 minutes on and 3 hrs 45 minutes off (tank 4). All four tanks were under the same hydraulic loading rate of 5 cm/day. After 165 days the reduction of total Kjeldahl nitrogen and ammonia nitrogen and the increase of nitrate nitrogen were greatest in tank 4, which had the shortest feeding period, while the continuous flow produced the lowest results. Effluent tanks 2 and 3 experienced similar levels of nitrification, both higher than that of tank 1. Thus supporting the idea that rapid dosing periods provide better aerobic conditions resulting in enhanced nitrification within the bed. Tank 4 had the highest removal rates for COD, and the continuous flow had the lowest. Tank 2 also exhibited a higher COD removal rate than tank 3, demonstrating that short dosing periods provide better within-bed oxidation and therefore offer higher removal efficiency.     

The ecological value of constructed wetlands for treating urban runoff.

The Sweetwater Authority's urban runoff diversion system (URDS) comprises constructed wetlands on a hillside between the town of Spring Valley and the Sweetwater Reservoir, California, USA. The URDS were designed to divert dry-weather and first-flush urban runoff flows from the Sweetwater reservoir. However, these constructed wetlands have developed into ecologically valuable habitat. This paper evaluates the following ecological questions related to the URDS: (1) the natural development of the species present and their growth pattern; (2) the biodiversity and pollutant stress on the plants and invertebrates; and (3) the question of habitat provided for endangered species. The URDS wetlands are comprised primarily of rush (Scirpus spp.) and cattails (Typha spp.). This vegetative cover ranged from 39-78% of the area of the individual wetland ponds. Current analyses of plant tissues and wetland sediment indicates the importance of sediment sorption for metals and plant uptake of nutrients. Analyses of URDS water following runoff events show the URDS wetlands do reduce the amount of nutrients and metals in the water column. Invertebrate surveys of the wetland ponds revealed lower habitat quality and environmental stress compared to unpolluted natural habitat. The value of the wetlands as wildlife habitat is constrained by low plant biodiversity and pollution stress from the runoff. Since the primary Sweetwater Authority goal is to maintain good water quality for drinking, any secondary utilization of URDS habitat by species (endangered or otherwise) is deemed an added benefit.     

人工湿地不同水流方式对生活污水净化的比较

通过小型复合流式人工湿地实验,监测了CODcr、TN、TP、NO3--N、NH4 -N等指标,旨在通过实验,找到处理污水的最佳水流方式.结果表明,垂直流和垂直流搭配对CODCr、TN、NH4 -N去除最好;而潜流和潜流搭配对NO3--N去除最好.人工湿地基质是影响磷的处理效果的主要因素,通过合理的操作方式可以最终从污水中除磷.在复合型人工湿地中延长水力停留时间能增加污染物的去除率.     

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.     

人工湿地污水处理技术研究进展

文章对人工湿地污水处理技术国内外研究现状进行了概迷,阐述了人工湿地污水处理技术主要研究内容及进展,包括人工湿地对污染物的去除机理、去除效率研究,影响人工湿地处理效率的因素研究.根据人工湿地在污水处理中的研究和应用现状,指出了今后的研究方向.     

厌氧—接触氧化渠—垂直潜流型人工湿地处理农村生活污水研究

选择厌氧—接触氧化渠—垂直潜流型人工湿地工艺处理农村生活污水,分析比较了各工艺段DO水平,接触氧化渠充氧效果明显.通过对COD、NH3—N和TP浓度及去除率的研究发现,厌氧池去除率较稳定,对各污染物去除率最高可达72％、49.54％和66.36％,接触氧化渠和人工湿地对各污染物也有较高去除率,但并不稳定.系统运行稳定后,出水水质整体可达到《城镇污水处理厂污染物排放标准》(GB 18918-2002)二级标准,部分时段可达一级B标准.     

潜流人工湿地处理城市污水氮和有机物的研究

在自行建造的模拟人工湿地装置上,通过改变水位来控制小型潜流人工湿地DO浓度,从而提高处理效率。试验中两种水位变化的运行都降低了人工湿地的氮和有机物,特别是对氮有较好的去除效果。第1阶段水位小幅度变化,出水DO浓度主要在2～4mg/L之间,COD、BOD5、TN、TKN去除率分别在85%～93%,91%～95%,65%～75%和75%～85%之间;第2阶段水位大幅度变化,出水DO浓度主要在1～4mg/L之间,COD、BOD5、TN、TKN去除率分别在80%～88%,85%～90%,70%～80%和80%～90%之间。     

Diversity of ammonia oxidising bacteria in a vertical flow constructed wetland.

Vertical flow constructed wetlands (VFCWs) with intermittent loading are very suitable for nitrification. Ammonia oxidising bacteria (AOB) are the limiting step of nitration. Therefore the AOB community of a full-scale VFCW, receiving municipal wastewater, was investigated within this study. The diversity of the functional gene encoding the alpha-subunit of the ammonia monooxygenase (amoA), present only in AOB, was assessed by denaturing gradient gel electrophoresis (DGGE). Only very few amoA sequence types dominated the wetland filter substrate; nevertheless a stable nitrification performance could be observed. During the cold season the nitrification was slightly reduced, but it has been shown that the same AOB could be identified. No spatial AOB pattern could be observed within the filter body of the VFCW. The most prominent bands were excised from DGGE gels and sequenced. Sequence analyses revealed two dominant AOB lineages: Nitrosomonas europaea/"Nitrosococcus mobilis" and Nitrosospira. Species of the Nitrosomonas lineage are commonly found in conventional wastewater treatment plants (WWTPs). In contrast, members of the Nitrosospira lineage are rarely present in WWTPs. Our observations indicate that the AOB community in this VFCW is similar to that found in horizontal flow constructed wetlands, but differs from common WWTPs regarding the presence of Nitrosospira.