Design Methodology of Free Water Surface Constructed Wetlands

Simple criteria, guidelines and models are established for free water surface (FWS) constructed wetland selection and preliminary sizing. The analysis employs models for FWS constructed wetland design, considering simultaneously the removal requirements and the hydraulics of the system. On the basis of these models, a step-by-step methodology is developed outlining the design procedure for new and performance evaluation for existing FWS constructed wetland systems. This methodology is combined with simple equations predicting the maximum wetland capacity in summer, so as to assist designers in sizing installations in tourist areas with increased summer populations. Furthermore, this methodology is further simplified, based on sensitivity analysis of the unit area requirements for wastewaters of various strengths, and various design conditions and performance criteria. In addition, comparison of the unit area requirements of FWS constructed wetland systems, subsurface flow (SF) constructed wetland systems and stabilization pond systems for wastewaters of various strengths and design conditions, provides designers with general guidelines concerning the preliminary selection between alternative natural treatment systems in areas where the use of natural systems is favored because of their low-cost, simple operation and high removal performance.     

Analysis of pollutant removal effect usinginnovative ridge-shaped constructed wetland

In this paper,a new type of ridge-shaped constructed wetland which combines surface flow and horizontal subsurface flow was proposed.The proposed wetland had simple structure,low construction and operating cost,less human interference and good pollution removal effect.The combination of surface flow and subsurface flow provided an aerobic and anaerobic alternating environment for the entire wetland.The performance of the proposed wetland was compared with a traditional horizontal subsurface flow wetland.The comparison results showed that the removal rates of BOD(biochemical oxygen demand),TN(total nitrogen),and TP(total phosphorus)in the ridge-shaped wetland increased up to 20.3%,17.0%,and 9.1%,respectively.The proposed wetland structure could be widely applied for treatment of rural and urban domestic sewage pollution or agricultural point and nonpoint source water pollution.     

温度和基质对人工湿地脱氮除磷效果的影响

构建由潜流人工湿地和表流人工湿地串联而成的复合人工湿地系统,研究了复合人工湿地脱氮除磷效果以及温度和基质对人工湿地脱氮除磷效果的影响。结果表明,复合人工湿地TP、氨氮平均去除率为33.64%、57.24%;水温降低会导致人工湿地氮磷去除率下降;基质为粗砂的潜流人工湿地脱氮除磷能力大于基质为砾石的潜流人工湿地。     

Experimental study of a novel hybrid constructed wetland for water reuse and its application in Southern China

A new type of hybrid constructed wetland (CW), consisting of both vertical-baffled flow wetland (VBFW) and horizontal subsurface flow wetland (HSFW), has been deployed in Southern China to naturally accelerate the removal of organic matter and nitrogen. The hybrid CW system is characterised by a combination of continuous baffled flow vertical wetland and 'S' pattern horizontal subsurface flow wetland with natural aeration ditches to increase the concentration of dissolved oxygen in the HSFW bed. An internal circulatory system from the HSFW effluent back to the VBFW may optionally be operated to enhance the biological denitrification effect. Cyperus alternifolius is the main macrophyte in the wetland bed. The performance of the hybrid CW was studied with a pilot-scale system and three full-scale systems for municipal sewage treatment in Southern China. The results suggest that this new hybrid CW can achieve removal efficiencies of chemical oxygen demand, suspended solids, ammonia nitrogen, total nitrogen, and total phosphorus of better than 83.6, 95.0, 71.7, 64.5 and 68.1% respectively, with a specific wetland bed area of 0.70-0.93 m(2) PE(-1). The mean effluent concentrations of these parameters would meet the regulatory discharge limits for wastewater treatment systems (GB18918, 2002) and reuse in the context of agricultural irrigation solutions in China.     

Twenty years experience with constructed wetland systems in Denmark--what did we learn?

Full scale constructed wetland systems for wastewater treatment have been in operation in Denmark since 1983, mainly for the treatment of domestic sewage from small villages. The systems are constructed as soil-based horizontal subsurface flow systems but, because of low soil hydraulic conductivity, surface runoff is evident in most of the systems. Two decades of experience show that soil-based systems are generally efficient in removing suspended solids and BOD, but the removal of nitrogen and phosphorus is lower (typically 30-50%) and the systems do not nitrify ammonium. Contrary to earlier claims, the reeds do not increase the hydraulic conductivity of cohesive soils as much as necessary to secure sub-surface flow. Operation needs of soil-based reed beds are low and normally restricted to emptying of the sedimentation tank, cleaning of the distribution system and mowing of the grass around the system. The dead plant material and accumulated litter on the surface of the systems improve performance after the initial years. A significant number of systems have been shut down or extended with other technologies in order to meet new effluent standards, particularly demands for nitrification. New constructed wetland systems are either compact vertical flow systems which provide good nitrification, willow systems with no discharge or restored wetland systems for nitrate removal. If efficient removal of phosphorus is required, this is achieved by chemical precipitation in the sedimentation tank.     

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)。     

Wastewater treatment in tsunami affected areas of Thailand by constructed wetlands.

The tsunami of December 2004 destroyed infrastructure in many coastal areas in South-East Asia. In January 2005, the Danish Government gave a tsunami relief grant to Thailand to re-establish the wastewater management services in some of the areas affected by the tsunami. This paper describes the systems which have been built at three locations: (a) Baan Pru Teau: A newly-built township for tsunami victims which was constructed with the contribution of the Thai Red Cross. Conventional septic tanks were installed for the treatment of blackwater from each household and its effluent and grey water (40 m3/day) are collected and treated at a 220 m2 subsurface flow constructed wetland. (b) Koh Phi Phi Don island: A wastewater collection system for the main business and hotel area of the island, a pumping station and a pressure pipe to the treatment facility, a multi-stage constructed wetland system and a system for reuse of treated wastewater. The constructed wetland system (capacity 400 m3/day) consists of vertical flow, horizontal subsurface flow, free water surface flow and pond units. Because the treatment plant is surrounded by resorts, restaurants and shops, the constructed wetland systems are designed with terrains as scenic landscaping. (c) Patong: A 5,000 m2 constructed wetland system has been established to treat polluted water from drainage canals which collect overflow from septic tanks and grey water from residential areas. It is envisaged that these three systems will serve as prototype demonstration systems for appropriate wastewater management in Thailand and other tropical countries.     

Analysis of pollutant removal effect using innovative ridge2shaped constructed wetland

In t his paper, a new t ype of ridg e2shaped co nstr ucted w etland w hich combines surface flow and ho rizontal subsurface flow w as proposed. The pro po sed wetland had simple str ucture, low co nstr uction and operating cost, less human interference and go od po llution remov al effect. T he combination of surface flow and subsurface flow pr ov ided an aero bic and anaerobic alter nating env iro nment for the entir e w etland. The performance of the proposed wetland was compared with a traditional horizontal subsurface flow wetland. The comparison results showed that the removal rates of BOD ( biochemical ox ygen demand) , T N ( t otal nitr ogen) , and T P ( tota l phospho rus) in the ridge2shaped w etland in2 creased up to 201 3% , 171 0% , and 91 1% , respectively . The pr oposed w et land structure co uld be w idely applied for t reatment of rur al and urban domest ic sew age pollutio n o r ag ricultural po int and no npo int so ur ce water po llut ion.     

Hydraulic performance of a modified constructed wetland system through a CFD-based approach

Low-cost household technologies, as horizontal subsurface flow constructed wetlands, are important to address water and sanitation needs in the Asia-Pacific region in a more integrated and sustainable manner, and a better understanding of these technologies would benefit their engineering design. Computational Fluid Dynamics (CFD) simulations of a modified constructed wetland system (EvaTAC) were undertaken to determine empirical effects of geometric and flow parameters on the hydraulic performance and the effluent pollutant fraction. The CFD model was validated by comparing the computed residence time distribution (RTD) with experimental results. RTD functions were then used to quantify hydraulic indexes: short-circuiting, mixing, and moment. The EvaTAC is composed of an evapotranspiration and treatment chamber (CEvaT) and a horizontal subsurface flow constructed wetland (HSSF-CW). For the CEvaT, length and the interaction between length and flow rate were the most important factors for the hydraulic efficiency. For the effluent pollutant fraction, the most important factor was flow rate. For the HSSF-CW, the strongest influence on the hydraulic efficiency was the length. Baffles and the interaction between length and baffles also had significant statistical influence on the hydraulic efficiency. Furthermore, the results showed that flow rate, length, and the interaction between flow rate and length influenced the effluent pollutant fraction significantly. Finally, a poor correlation between hydraulic indexes and effluent pollutant fraction was obtained, indicating that the hydraulic indexes are not good predictors of the effluent pollutant fraction.     

堵塞对湿地内水流流态及污水处理效果的影响

通过在污水中加入氯化钠示踪剂,研究人工湿地及其对照系统内水力停留时间的分布(HRTD),探讨潜流人工湿地和垂直流人工湿地中植物在堵塞前后对水流流态的影响,探讨堵塞对上述两种人工湿地水流流态的影响。结果表明:对于潜流人工湿地(SFCW),堵塞前湿地植物缩短了水力停留时间(HRT),堵塞后延长了HRT;对于垂直流人工湿地(VFCW),堵塞前湿地植物对水流流态无明显影响,堵塞后延长了湿地内的HRT。堵塞对湿地内水流流态影响明显,潜流和垂直流湿地由于堵塞其HRT分别延长了12.3%,22.6%。堵塞后湿地对污水的净化能力都要强于堵塞前,但是湿地的污水处理量减小,堵塞严重时湿地丧失其污水净化功能。     

Influence of design, physico-chemical and environmental parameters on pharmaceuticals and fragrances removal by constructed wetlands

The ability of several mesocosm-scale and full-scale constructed wetlands (CWs) to remove pharmaceuticals and personal care products (PPCPs) from urban wastewater was assessed. The results of three previous works were considered as a whole to find common patterns in PPCP removal. The experiment took place outdoors under winter and summer conditions. The mesocosm-scale CWs differed in some design parameters, namely the presence of plants, the vegetal species chosen (Typha angustifolia versus Phragmites australis), the flow configuration (surface flow versus subsurface flow), the primary treatment (sedimentation tank versus HUSB), the feeding regime (batch flow versus continuous saturation) and the presence of gravel bed. The full-scale CWs consisted of a combination of various subsystems (ponds, surface flow CWs and subsurface flow CWs). The studied PPCPs were ketoprofen, naproxen, ibuprofen, diclofenac, salicylic acid, carbamazepine, caffeine, methyl dihydrojasmonate, galaxolide and tonalide. The performance of the evaluated treatment systems was compound dependent and varied as a function of the CW-configuration. In addition, PPCP removal efficiencies were lower during winter. The presence of plants favoured naproxen, ibuprofen, diclofenac, salicylic acid, caffeine, methyl dihydrojasmonate, galaxolide and tonalide removal. Significant positive correlations were observed between the removal of most PPCPs and temperature or redox potential. Accordingly, microbiological pathways appear to be the most likely degradation route for the target PPCPs in the CWs studied.     

Nutrient reduction evaluation of sewage effluent treatment options for small communities.

Small communities that are sewered by either package sewage treatment plants or on-site sewerage facilities are finding that the ground and surface waters are being contaminated. Nitrogen, which typically is not removed in these conventional systems, is a major concern. This project evaluated the capability of four sewage treatment technologies to reduce the amount of nitrogen being discharged in the effluent to the receiving environment. The four sewage treatment processes evaluated include a recirculating sand filter, biofilter, slow sand filter and constructed subsurface flow wetland. These processes were evaluated for their capability to reduce nitrogen, phosphorus, BOD5 and TSS. The primary objective of the project was to evaluate the capability of these treatment processes to reduce nitrogen using biological processes nitrification and denitrification. This paper reports on the performance of these processes to reduce nitrogen. The study demonstrated that the biofilter was capable of removing from a primary treated influent 40% of the total nitrogen. For the same quality influent the recirculating sand filter was capable of removing 35% of the total nitrogen. Secondary treated effluent was fed to the slow sand filter and the subsurface flow wetland. There was a 52% reduction in total nitrogen through the wetland however there was virtually no reduction in total nitrogen through the slow sand filter.     

城市湖泊污水处理的实验分析

以西安市兴庆湖为研究对象,对湖泊的水质进行了水平潜流和自由表面流净化的实验研究,比较了两种湿地的净化效果。在相同的水力负荷、水力停留时间、水深等条件下,分析了两种人工湿地对城市湖泊中的有机物、氮、磷等主要污染物的净化效果,及不同影响因素对系统处理效果的影响,比较了两种人工湿地的优缺点。     

Enhanced P, N and C removal from domestic wastewater using constructed wetland employing construction solid waste (CSW) as main substrate

Construction solid waste (CSW), an inescapable by-product of the construction and demolition process, was used as main substrate in a four-stage vertical subsurface flow constructed wetland system to improve phosphorus P removal from domestic wastewater. A 'tidal flow' operation was also employed in the treatment system. Under a hydraulic loading rate (HLR) of 0.76 m3/m2 d for 1st and 3rd stage and HLR of 0.04 m3/m2 d for 2nd and 4th stage of the constructed wetland system respectively and tidal flow operation strategy, average removal efficiencies of 99.4% for P, 95.4% for ammoniacal-nitrogen, 56.5% for total nitrogen and 84.5% for total chemical oxygen demand were achieved during the operation period. The CSW-based constructed wetland system presents excellent P removal performance. The adoption of tidal flow strategy creates the aerobic/anoxic condition intermittently in the treatment system. This can achieve better oxygen transfer and hence lead to more complete nitrification and organic matter removal and enhanced denitrification. Overall, the CSW-based tidal flow constructed wetland system holds great promise for enabling high rate removal of P, ammoniacal-nitrogen and organic matter from domestic wastewater, and transforms CSW from a waste into a useful material.     

BTEX degradation in a cold-climate wetland system.

A pilot-scale subsurface vertical-flow wetland system was constructed at the former BP Refinery in Casper, Wyoming in order to determine benzene, toluene, ethylbenzene and xylene (BTEX) degradation rates in a cold-climate application. The pilot system, consisting of 4 cells, each dosed at a nominal flow rate of 5.4 cubic metres per day, was operated between August and December 2002. The pilot tested the effects of wetland mulch and aeration on system performance. Areal rate constants (kA values) were calculated based on an assumed three tanks in series (3TIS). The presence of wetland sod and aeration both improved treatment performance. Mean kA values were 244 m/yr for cells without sod or aeration, and improved to 356 m/yr for cells with sod and aeration. Based on the results of the pilot system, a full-scale wetland system (capable of operating at 6,000 m3/day) was started up in May 2003. The full-scale system achieved permit compliance within one week of startup, but is currently being loaded at only 45% of the design hydraulic load, and 15% of the design BTEX mass load, resulting in a mean kA value of approximately 350 m/yr.     

Sustainability of Natural and Mechanized Aerated Ponds for Domestic and Municipal Wastewater Treatment in Palestine

Abstract

More than half of the current wastewater treatment facilities constructed in Palestine are waste stabilization ponds (WSP) and have several problems in their operation. This article evaluates three selected case studies on the various pond systems including WSP, algae- and duckweed-based ponds (ABP and DBP, respectively) and one mechanically aerated lagoon (AL) system. The effects of various design and operating parameters on the pond system' performance, with special emphasis on nitrogen removal, are discussed. The effluent quality of WSP and AL complies only with BOD limits, but not with microbiological limits prescribed for agricultural purposes, as determined by national standards. ABP and DBP achieved nitrogen removal only under high surface area demand (5-7 m2capita-1). Suitable plans for modifying existing aerated lagoons or for upgrading natural lagoons are suggested in order to comply with microbiological standards for effluent use in restricted irrigation. Finally, the suggested sustainability criteria for the evaluated pond systems may help the decision makers, as well as their designers and donor countries, to better select and design low-cost treatment options for sustainable wastewater management in developing countries.     

中水湿地去氮效果研究

以山东省平阴中水湿地为研究对象,通过对湿地水体、底泥的氨态氮(NH3-N)、硝态氮(NO3--N)沿程变化的分析,研究湿地对中水中氮(N)的去除效果。结果表明:湿地对水体中NH3-N的去除效果较好,而作为水体中N主要存在形式的NO3--N沿水流方向却呈增加趋势,微生物硝化作用强烈。底泥中总氮(TN)沿水流方向也呈增加趋势,累计效应比较明显。研究结果为湿地设计的进一步改进提供理论支持。     

人工湿地在城市水污染治理中的应用

人工湿地污水处理是由相互关联的基质、植物和微生物通过物理、化学、生物过程的协同作用完成的,它只需要投入极少的人力和能源,就可以去除有机污染物、营养物质、固体悬浮物、重金属物质,实现对生活污水、面源污染径流、农田废水、二级污水处理厂出水、河道末端水进行长期稳定的净化处理。目前,该工艺在郑州和成都得到了应用,均取得了很好的效果,然而人工湿地在城市水污染治理中还存在有机质积累、占地面积大、受季节影响等问题。人工湿地是耐用而高效的系统,不断完善人工湿地的设计、性能、操作及维护,将能够更有效地改善水质。     

NUMERICAL ANALYSIS OF THE PERFORMANCE OF HORIZONTAL AND WAVY SUBSURFACE FLOW CONSTRUCTED WETLANDS

A three-dimensional numerical model is proposed for modeling the TP transport in the Horizontal Subsurface Flow(HSSF) and Wavy subsurface Flow(WSSF) constructed wetland in this article.Both numerical simulations and physical experiments indicate that the removal efficiency of WSSF is higher than that of HSSF.The difference of performance in removing pollutants,e.g.,Total Phosphorus(TP),between HSSF and WSSF is numerically analyzed from three interactive aspects,that is,the hydraulic behavior,the substrate a...     

The performance of vertical flow constructed wetland systems with special reference to the significance of oxygen transfer and hydraulic loading rates.

The paper reviews the development of the vertical flow (VF) reed beds/constructed wetlands over the past 20 years. The performance of VF systems (and their use within hybrid systems) is analysed by reference to a number of brief case studies. The oxygen transfer rate (OTR) achieved is absolutely critical to the sizing of the systems. The author reviews the reported OTRs and comments on the existing design equations proposed for calculation of the area of beds. The 1st generation of VF systems used a set of parallel beds that were dosed one at a time in rotation and then rested for a period of days because there was considerable concern (based on early experience) that they would become clogged. In the past 10 years a number of new designs of 2nd generation VF beds have been built which make use of a single bed and hence operate without any resting periods. The hydraulic loading rate and the selection of the bed media, which are critical to the design and hence successful operation of these 2nd generation compact VF beds, are described. It is now possible to produce a very high quality of effluent from VF beds alone sized at 2 m2/pe when treating domestic sewage.