净水技术 EPA技术说明——人工自由水面湿地

美国EPA提供了一系列适用于污水处理系统的技术说明文件，供学习参考。

原文出处：EPA

翻译：阮辰旼、何雪妮

Wastewater Technology Fact Sheet

污水处理技术概况—人工自由水面湿地

Free water surface (FWS) wetlands are defined as wetland systems where the water surface is exposed to the atmosphere. Most natural wetlands are FWS systems, including bogs (primary vegetation mosses), swamps (primary vegetation trees), and marshes (primary vegetation grasses and emergent macrophytes.) The observation of water quality improvements in these natural wetlands for many years led to the development of constructed wetlands in an effort to replicate the water quality and habitat benefits of natural wetlands in a constructed ecosystem. The majority of FWS constructed wetlands designed for wastewater treatment are marshes, but a few operating examples of bogs and swamps exist. In FWS treatment wetlands, water flows over a vegetated soil surface from an inlet point to an outlet point. In some cases, water is completely lost to evapotranspiration and seepage within the wetland. A diagram of FWS wetland is shown in Figure 1.

自由水面（FWS）湿地是指水面直接暴露在大气中的湿地系统。大多数天然湿地都是FWS系统，包括主要植被为苔藓的沼泽、主要植被为树木的沼泽和主要植被为草和水生大型植物的沼泽。多年来对这些天然湿地水质改善的观察研究促成了人工湿地的发展，使人们致力于在建造仿生态系统的过程中复制天然湿地的水质和生态效益。大多数为污水处理而设计的FWS建造的湿地都是主要植被为草和水生大型植物的沼泽，但也有一些主要植被为苔藓的沼泽和主要植被为树木的沼泽的运行实例。在FWS湿地的污水处理过程中，污水在覆盖植被的土壤表面上从进水点流到出水点。在某些情况下，水也会在湿地内直接蒸发和渗漏。图1显示了FWS湿地的图示。

There are relatively few examples of the use of natural wetlands for  wastewater treatment in the United States. Because  any discharge to a natural wetland must satisfy National Pollutant Discharge Elimination System (NPDES) limits, these wetlands are typically used for advanced wastewater treatment (AWT) or tertiary polishing. The design goals for constructed wetlands range from an exclusive commitment for basic treatment functions to systems which provide advanced treatment and/or combine with enhanced wildlife habitat and public recreational opportunities.  The size of the FWS wetland systems ranges from small on-site units designed to treat septic tank effluents to large units with more than 16,188 hectares (40,000 acres).  A large system is being used to treat phosphorus from agricultural storm water drainage in south Florida.  Operational FWS wetlands designed for municipal wastewater treatment in the United States  range from less than 3785 liters per day (1,000 gallons per day) to more than 75,708 m ³ /day (20 million gallons per day).

在美国，利用自然湿地进行污水处理的例子相对较少。因为任何向自然湿地进行的排放都必须满足国家污染物排放清洁系统（NPDES）的限制，这些湿地通常只能用于深度污水处理（AWT）或三级处理。人工湿地的设计目标已从实现基本处理功能的单一系统目标，提高到能够提供深度处理和/或与增强野生动物栖息地和公共休闲娱乐相结合的综合系统的目标。FWS湿地系统的规模一般可以从设计仅用于处理化粪池污水的小型现场系统到超过16188公顷（40000英亩）的大型系统，比如一个大型系统正被用来处理佛罗里达州南部农业排水中的磷。在美国，为城市污水处理而设计的运行中的FWS湿地的规模，已从每天不到3785升（每天1000加仑）到超过75708立方米/天（每天2000万加仑）。

Constructed FWS wetlands typically consist of one or more shallow basins or channels with a barrier to prevent seepage to sensitive ground waters and a submerged soil layer to support the roots of the selected emergent macrophyte vegetation.  Each system has appropriate inlet and outlet structures to ensure uniform distribution and collection of the applied wastewater.   The most commonly used emergent vegetations in constructed FWS wetlands include cattail (Typha spp.), bulrush (Scirpus spp.), and reeds (Phragmites spp.).  In systems designed primarily for treatment, it is common to select only one or two species for planting.  The plant canopy formed by the emergent vegetation shades the water surface, preventing growth and persistence of algae, and reduces wind-induced turbulence in the water flowing through the system.    Perhaps most important are the submerged portions of the living plants, the standing dead plants, and the litter accumulated from previous growth. These submerged surfaces provide the physical substrate for the periphytic-attached growth organisms responsible for much of the biological treatment in the system.   The water depth in the vegetated portions of these systems ranges from a few inches to two feet or more.

人工FWS湿地通常由一个或多个浅水盆地或渠道组成，其中设置护堤作为屏障防止污水渗入更为敏感的地下水，淹没的土壤层来固定选定的水生大型植被的根部。每个系统都有适当的入口和出口结构，以确保待处理的污水被均匀分布和收集。在人工FWS湿地中，最常用的水生植被包括香蒲(Typha spp.)、牛筋草(Scirpus spp.)和芦苇(Phragmites spp.)。在主要为污水处理而设计的系统中，通常只选择一个或两个物种进行种植。新生植被形成的植物冠层可以遮蔽水面，防止藻类的生长和持续繁殖，并可以减少流经系统的水由风力引起的湍流。系统中最重要的是活体植物的淹没部分、还未倾倒的已死亡的植物，以及之前散落积累的残枝。这些淹没在水面以下的有机物为负责系统中大部分生物处理过程的微生物提供了物理基质，淹没系统中植被部分的水深从几英寸到两英尺或更深。

The influent to these wetlands spreads over a large area of shallow water and emergent vegetation. The subsequent low velocity and essentially laminar flow provides for very effective particulate removal in the front part of the system.  This particulate material, characterized as total suspended solids (TSS), contains Biochemical Oxygen Demand (BOD) components, fixed forms of total nitrogen (TN) and total phosphorus (TP), and trace levels of metals and more complex organics.   The oxidation or reduction of these particulates releases soluble forms of BOD, TN, and TP to the wetland environment, which are available for adsorption by the soils and removal by the active microbial and plant populations throughout the wetland. Oxygen is available at the water surface, microsites on living plant surfaces, and on root and rhizome surfaces, allowing some aerobic activity the wetland.  It is, however, prudent to assume that the bulk of the liquid in the FWS wetland is anoxic or anaerobic. The lack of oxygen can limit the biological removal of ammonia nitrogen (NH ₃ /NH ₄ -N) via nitrification, but the FWS wetland is still  effective for removal of BOD, TSS, trace metals, and some complex organics because the treatment of these occurs under both aerobic and anoxic conditions.

流入这些湿地的污水在大面积的浅水区和植被上扩散。随后污水较慢的低速流动和层流流态为前部的湿地系统提供了非常有效的颗粒物去除效果。这种颗粒物质的主要是总悬浮固体（TSS），含有生化需氧量（BOD）成分、固定形式的总氮（TN）和总磷（TP），以及微量的金属和其他复杂的有机物。这些颗粒物质经过氧化或还原将可溶性形式的BOD、TN和TP释放到湿地环境中，可被土壤吸附，并被整个湿地中活跃的微生物和植物种群清除。氧气在水面、活体植物表面、根和根茎表面的微生物中能够发挥作用，可以在湿地中提供好氧环境。然而，从最不利条件考虑，假设FWS湿地中的大部分液相都是缺氧或厌氧的，缺氧会限制通过硝化作用对氨氮（NH ₃ /NH ₄ -N）的生物去除，但不影响FWS湿地对BOD、TSS、微量金属和一些复杂的有机物的去除，因为这些反应都可以在好氧和缺氧条件下进行的。

If nitrogen removal and/or enhancement of wildlife habitat is a project goal, consideration should be given to alternating shallow water emergent vegetated zones with deeper (greater than 1.83 meters or six feet) water zones containing selected submerged vegetation. Deeper water zones provide a completely exposed water surface for atmospheric re-aeration and submerged vegetation provides an additional source of oxygen for nitrification.  The deeper water zones will also attract and retain a large variety of wildlife, particularly ducks and other water birds.    This concept, in use at Arcata, California, and Minot, North Dakota, can provide excellent treatment on a year-round basis in warm climates and on a seasonal basis in colder climates where low temperatures and ice formation occur. The hydraulic residence time (HRT) in each of the open water zones should be limited to about three days at design flow to prevent the re-emergence of algae.  Such systems should always start and end with shallow emergent vegetation zones to ensure retention and treatment of particulate matter and to minimize wildlife toxicity in the open water zones. The use of FWS constructed wetlands has increased significantly since the late 1980’s. The systems are widely distributed in the United States and are found in about 32 states.

如果同时将脱氮和/或提供野生动物栖息地作为一个项目的目标，应考虑将浅水区的水草植被与深水区（大于1.83米或6英尺）的水草植被交替使用。较深的深水区应该提供一个完全暴露于大气的水面，水下植被可以为硝化作用提供额外的氧气来源。较深的水区也可以引进和保留大量的野生动物，特别是鸭子和其他水鸟。这个概念在加利福尼亚州的阿卡塔和北达科他州的米诺特使用，实践发现可以在温暖的气候中全年提供良好的污水处理效果，在低温和结冰的寒冷气候中则是季节性发挥功效。在设计流量的范围内，每个开放水区的水力停留时间（HRT）应限制在3天左右，以防止藻类的出现和增殖。这样的系统的入口和出口都应该是种植有植被的浅水区，以确保能够截留和降解颗粒物质，并尽量减少对公众开放的水域范围内的野生动物带来的风险。自20世纪80年代末以来，人工FWS湿地的应用已大大增加，这些系统在美国广泛分布，在大约32个州都有。

In the United States, it is routine to provide some preliminary treatment prior to a FWS wetland. The minimal acceptable level is the equivalent of primary treatment which can be achieved with septic tanks, with Imhoff tanks for smaller systems, or with deep ponds with a short HRT. About 45 percent of operational FWS wetland systems use facultative lagoons for preliminary treatment, but these systems have also been used behind other treatment systems. For example, some of the largest FWS systems, in Florida and Nevada, were designed for tertiary effluent polishing and receive effluent from mechanical AWT plants.

在美国，FWS湿地之前进行一些预处理是常规做法。预处理期望达到的最基本处理水平可通过化粪池、小型的英霍夫池（Imhoff tank）或停留时间较短的深层池来实现。大约45%正在运行中的FWS湿地系统都会使用调蓄池进行预处理，这些调蓄池也可以是被用于其他处理系统之后的缓冲。例如，在佛罗里达州和内华达州，一些最大的FWS系统被设计为三级污水处理，并接收来自深度处理工艺污水处理厂的排放出水。

Non-discharging, total retention FWS systems have been used in arid parts of the United States where the water is completely lost through a combination of seepage and evapotranspiration. These systems require that attention be paid to the long term accumulation of salts and other substances which might become toxic to wildlife or plants in the system.  While it is impossible to exclude wildlife from FWS wetlands, it is prudent to minimize their presence until the water quality approaches secondary levels of treatment.  This can be accomplished by limiting open water zones to the latter part of the system and using dense stands of emergent vegetation in the front part of the wetland. Selecting vegetation with little food value for animals or birds may also help. In colder climates or where large land areas are not available for wetland removal of nitrogen, a smaller wetland system can be designed for BOD/TSS removal. Nitrogen removal can be achieved with a separate process. Wetland systems in Kentucky and Louisiana successfully use an integrated gravel trickling filter for nitrification of wastewater ammonia. Seasonally operated FWS wetlands are also used in very cold climates, in which the wastewater is retained in a lagoon during the winter months and discharged to the wetland at a controlled rate during the warm summer months.

无排放、全消纳的FWS湿地系统已经在部分的美国干旱地区被应用，这些系统中所有的水分都通过渗漏和蒸发完全流失，但需要特别注意盐分和其他物质在湿地中的长期积累，这些物质可能对系统中的野生动物或植物产生毒性。虽然不可能将野生动物完全排除在FWS湿地之外，但谨慎的做法是尽量减少它们的存在，直到湿地中的质接近二级处理水平。这可以通过将开放水域设计在系统的后半部分，以及在湿地的前半部分种植密集的水生植被来实现，此外，选择对动物或鸟类没有什么食物价值的植被也会有所帮助。在气候较冷或没有大面积土地可发挥脱氮作用的地方，可以设计一个较小的湿地系统来去除BOD/TSS。氮的去除可以通过另外一个单独的过程来实现。肯塔基州和路易斯安那州的湿地系统成功地使用了一体化的砾石涓流过滤器对污水中的氨进行硝化处理。在非常寒冷气候条件下的地区，季节性运行的FWS湿地通常被应用，污水被保留在一个蓄水池塘中。在这种寒冷的运行情况下，污水在冬季储存在蓄水池塘中，并在夏季时以可控的速度排放到排放到湿地中。

FWS wetlands require a relatively large land area, especially if nitrogen or phosphorus removal is required.  The treatment is effective and requires little in the way of  mechanical equipment, energy, and skilled operator attention. Wetland systems can be a most cost effective treatment alternative where suitable land is available at reasonable cost.  They also provide enhanced habitat and recreational values. Land requirements and costs tend to favor application of FWS technology in rural areas.

FWS湿地需要一个相对较大的土地面积，特别是在需要去除氮或磷的情况下。在有合适的土地和合理的成本的情况下，这种湿地系统的处理方法是有效的，而且不需要什么机械设备、能源和熟练的操作人员的关注，可以是一个最具成本效益的处理选择。它们还能提供动物栖息地和公众娱乐的价值。FWS湿地系统对土地的要求和成本的需求气矿也更适合在农村地区应用。

FWS wetland systems reliably remove BOD, Chemical Oxygen Demand (COD), and TSS. With a sufficiently long HRT, they can also produce low levels of nitrogen and phosphorus. Metals are also removed and a reduction in fecal coliforms of about a one log can be expected. In addition to municipal wastewaters, FWS systems are used to treat mine drainage, urban storm water, combined sewer overflows, agricultural runoff, livestock and poultry wastes, landfill leachates, and for mitigation purposes.   Because the water is exposed and accessible to humans and animals, the FWS concept of receiving partially treated wastewater may not be suited for use in individual homes, parks, playgrounds, or similar public facilities.  A gravel bed subsurface flow (SF) wetland is a choice for these applications.

FWS湿地系统能可靠地去除BOD、化学需氧量（COD）和TSS。如果有足够长的水力停留时间，它们也可以去除一定水平的氮和磷，此外，金属也能被去除，粪便大肠菌群可以降低约一个数量级。除了城市污水，FWS系统还被用来处理矿井排水、城市暴雨径流、合流排水溢流、农业径流、牲畜和家禽废物，以及垃圾填埋场渗滤液。由于FWS湿地系统的水面是直接暴露的，可以被人类和动物接触到，用于处理污水的FWS湿地可能不适合用于个人住宅、公园、游乐场或类似的公共设施，相对而言，人工潜流（SF）湿地更为适用。

Some advantages and disadvantages of FWS wetlands are listed below:

以下是FWS湿地的一些优势和劣势：

Advantages

优点

? FWS wetlands offer effective treatment in a passive manner, minimizing mechanical equipment, energy, and skilled operator requirements.

?  FWS湿地以被动运行的方式提供了有效的污水处理，而且减少了机械设备、能源的消耗，也不依赖于熟练操作人员的投入。

? FWS wetlands may be less expensive to construct, and are less costly to operate and maintain than conventional mechanical treatment systems.

?  与传统的机械处理系统相比，FWS湿地的建设成本较低，而且操作和维护成本也较低。

?  Year-round operation for secondary treatment is  possible in all but the coldest climates. Year-round operation for  advanced or tertiary treatment is possible in  warm to moderately temperate climates.

?  除了极端寒冷地区，所有的地方都可以全年达到二级处理水平。在温暖和中等温度的气候条件下，全年实现深度或三级处理都是可能的。

? Wetland systems provide a valuable addition to the “green space” in a community, and include the incorporation of wildlife habitat and public recreational opportunities.

?湿地系统为社区的“绿色空间”提供了宝贵的补充，并提供了野生动物栖息地和公共娱乐场所。

? Wetland systems produce no residual biosolids or sludges requiring subsequent treatment and disposal.

  ?  湿地系统不产生需要后续处理的残余生物固体或污泥。

? The removal of BOD, TSS, COD, metals, and persistent organics in   municipal wastewaters can be very effective with a reasonable detention time. The removal of nitrogen and phosphorus can also be effective with a significantly longer detention time.

?  在合理的水力停留时间内，湿地系统对城市污水中的BOD、TSS、COD、金属和持久性有机物的去除可以非常有效。氮和磷的去除也可以在更长的停留时间内有效去除。

Disadvantages

缺点

? The land area required for FWS wetlands can be large, especially if nitrogen or phosphorus removal are required.

?  FWS湿地所需的土地面积可能很大，特别是如果需要去除氮或磷。

? The removal of BOD, COD, and nitrogen are biological processes and essentially continuously renewable.  The phosphorus, metals, and   some   persistent   organics removed by the system are bound in the wetland sediments and accumulate over time.

?  去除BOD、COD和氮是生物过程，基本上是可持续的。该系统去除的磷、金属和一些持久性有机物会沉降在湿地沉积物中，并随着时间的推移而不断积累。

?  In cold climates low winter temperatures reduce the rate of removal for BOD and the biological reactions responsible for nitrification and denitrification. An increased detention time can compensate for this, but the increased wetland size required in extremely cold climates may not be cost effective or technically feasible.

?  在寒冷的气候条件下，冬季的低温会降低BOD的去除率以及停止硝化和反硝化的生物反应。增加停留时间可以弥补这一点，但在极度寒冷的气候下，增加湿地面积可能不符合成本效益或技术上的可行性。

?  The bulk water in most constructed FWS wetland systems is essentially anoxic, limiting the potential for rapid biological nitrification of ammonia. Increasing the wetland size and, therefore, the detention time, may compensate for this, but may not be cost effective. Alternate methods for nitrification in combination with a FWS wetland have performed successfully.

?  大多数人工FWS湿地系统中分散的水域基本上都是缺氧的，限制了快速生物硝化的潜力。增加湿地面积，从而增加滞留时间，可以弥补这一缺陷，但可能不具成本效益。与FWS湿地相结合的其他单独硝化工艺可以帮助实现这一目标。

?  Mosquitoes and other insect vectors can be a problem.

?  蚊子和其他昆虫病媒可能是一个问题。

?  The bird population in a FWS wetland can have adverse impacts if an airport is nearby.

?  如果附近有机场，FWS湿地中的鸟类数量会产生不利影响。

?  FWS constructed wetlands can remove fecal coliforms by at least one log from typical municipal wastewaters. This may not be sufficient to meet discharge limits in all locations and supplemental disinfection may be required. The situation is further complicated because birds and other wildlife in the wetland produce fecal coliforms.

?  人工FWS湿地可以从常见的城市污水中去除粪便大肠菌群，至少能降低一个数量级。但这可能仍不足以满足所有地点的排放限制，可能需要进行补充消毒。由于湿地中的鸟类和其他野生动物也会产生粪便大肠菌群，因此情况会更加复杂。

Published models for the pollutant removal design of FWS wetland systems have been available since the late 1980’s. More recent efforts have produced three textbooks containing design models for FWS wetlands (Reed, et al., 1995; Kadlec & Knight,  1996; Crites & Tchobanoglous, 1998)  All three models are based on first order plug flow kinetics but provide different results based on the use of different databases.  The Water Environment Federation (WEF) presents a comparison of the three approaches in the Manual of Practice  on Natural Systems (WEF, 2000.)  Another comparison is found in the U.S. EPA design manual on  wetland  systems  (U.S.  EPA,  2000.)   This manual also includes design models developed by Gearheart and Finney. The designer of a FWS wetland system should consult these references and select the method best suited for the project under consideration. A preliminary estimate of the land area required for an FWS wetland can be obtained from Table 1 of typical areal loading rates presented below.  These values can also be used to check the results from other references.

自20世纪80年代末以来，已有公开发布的SF湿地系统的设计模型。在20世纪90年代中后期，通过努力，出版了三本包含SF湿地设计模型的教材（Reed，et al 1995，Kadlec&Knight 1996，Crites&Tchobanoglous 1998）。在这三本教材中，模型都是基于一阶塞流的流体动力学，但由于作者开发工作的选择，并且由于没有使用相同的数据库来推导模型，结果并不总是一致。水环境联合会（WEF）在其《自然系统实践手册》（WEF，2000年）和美国环保局《湿地系统设计手册》（EPA，2000年）中对这三种模型方法进行了比较，该手册还包括Gearheart和Finney开发的设计模型。FWS湿地系统的设计者应该查阅这些参考资料，并选择最适合所设计项目的方法。SF湿地所需土地面积的初步估计可以从表1的典型单位面积的污染物负荷中获得，这些值也可用于复核前面引用的参考文献的结果。

The pollutant requiring the largest land area for removal determines the necessary treatment area for the wetland, which is the bottom surface area of the wetland cells.  The wastewater flow must be uniformly distributed over the entire surface for that area to be 100 percent effective. This is possible with constructed wetlands by careful grading of the bottom surface and the use of appropriate inlet and outlet structures.  Uniform distribution of wastewater is more difficult when natural wetlands are used for treatment or polishing. The existing configuration and topography are typically retained in these natural wetlands, which can result in significant short circuiting of flow.   Dye tracer studies in such wetlands have shown that the effective treatment area can be as little as 10 percent of the total wetland area.  The total treatment area should be divided into at least two cells for all but the smallest systems. Larger systems should have at least two parallel trains of cells to provide flexibility for management and maintenance.

所以待处理污染物中，需要最大土地面积的那个污染物，将决定湿地的占地面积。这个面积是指湿地的有效底表面积，为了使该面积范围中的湿地能100%发挥功效，污水流量必须均匀分布在整个湿地面积上。通过仔细平整底面和使用适当的入口和出口结构，建造的湿地可以做到这一点。除最小的系统外，湿地的有效区域应至少分为两个单元，较大的系统应至少有两组平行的单元，以便为管理和维护提供灵活性。

Wetland systems are living ecosystems. The life and death cycles of the biota produce residuals which can be measured as BOD, TSS, nitrogen, phosphorus, and fecal coliforms. As a result, regardless of the size of the wetland or the characteristics of the influent, there will always be a residual background concentration of these materials in wetland systems. Table 2 summarizes these background concentrations.

这些湿地系统本身都是活的生态系统，生物体经历繁殖生长和死亡，产生的残余物质会通过BOD、TSS、氮、磷和粪便大肠菌群来体现。因此，无论湿地的大小或进水的污染特征如何，在这些湿地系统中，湿地本身总是会含有一定的本地浓度。表2总结了这些污染物的本底浓度情况。

Because removal of BOD and various nitrogen forms is temperature dependent, the temperature of the wetland must be known for proper design. The water temperature in large systems with a long HRT (greater than 10 days) will approach the average air temperature except during subfreezing weather in the winter.   Methods to estimate the water temperature for wetlands with a shorter HRT (less than 10 days) can be found in the references cited.

因为BOD和各种氮的去除与温度有关，所以必须提前掌握湿地的温度情况以进行适当的设计。除了冬季的极端寒冷天气，具有长水力停留时间（大于10天）的大型系统的水温应接近平均气温。水力停留时间较短（<10天）的湿地的水温估算方法可在前面提到的已发表参考文献中找到。

Because living plants and litter provide significant frictional resistance to flow through the wetland , it is necessary to consider the hydraulic aspects of system design.  Manning’s equation is generally accepted as the model for the flow of water through FWS wetlands. Descriptive information is found in the references cited.  Flow resistance impacts the configuration selected for the wetland cell: the longer the flow path, the higher the resistance.  To avoid hydraulic problems, an aspect ratio (L:W) of 4:1 or less is recommended.

由于湿地中生长的植物和植物的残留物对流经的水流提供了很大的摩擦阻力，因此有必要考虑系统的水力方面设计。曼宁方程被普遍认为适用于FWS湿地的流体模型，相关信息可以在前序介绍的参考文献中找到。流动的阻力影响到为湿地单元选择的配置：流动路径越长，阻力就越大。为了避免上述水力问题，建议长宽比（长∶宽）为4∶1或更小。

A lightly loaded FWS wetland can achieve the “background” effluent levels shown in Table 2.  In general, an FWS constructed wetland is designed to produce a specified effluent quality. Table 1 can be used to estimate the size of the wetland necessary to produce the desired effluent quality.  The design models in the referenced publications provide a more precise estimate of required treatment area. Table 3 summarizes actual performance data for 27 FWS systems from a recent Technology Assessment (U.S. EPA, 2000).

较低污染负荷的SF湿地可以将污水处理达到表2中给出的本底限值水平。在一般情况下，FWS人工湿地通常可以根据特定的出水水质来进行设计，表1可用于简单估算达到目标出水水质所需的湿地面积大小。参考出版物中的设计模型可以将湿地的面积大小计算的更精确。表3总结了美国环保局技术评估（EPA，1993）的27个FWS湿地系统的实际性能数据情况。

In theory, the performance of a wetland system can be   influenced   by   hydrological   factors.   High evapotranspiration (ET) rates may increase effluent concentrations, but may also increase the HRT in the wetland.  High precipitation rates dilute the pollutant concentrations but also shorten the HRT in the wetland. In most temperate areas with a moderate climate, these influences are not critical for performance. Hydrological aspects only need to be considered for extreme values of ET and precipitation.

理论上，SF湿地系统的性能会受到水文因素的影响。高蒸发率(ET)可能会增加出水的浓度，但也会增加湿地的水力停留时间。高降水率稀释了湿地中的污染物浓度，但也缩短了湿地的水力停留时间。在大多数气候温和的温带地区，这些影响对湿地的污染物去除效率并不重要。这些水文方面的因素只需要考虑ET和降水的极端情况。

The routine operation and maintenance (O&M) requirements for FWS wetlands are similar to those for facultative lagoons. They include hydraulic and water depth control, inlet/outlet structure cleaning, grass mowing on berms, inspection of berm integrity, wetland vegetation management, mosquito and vector control (if necessary), and routine monitoring.

FWS湿地的常规操作和维护（O&M）要求与蓄水型的沼泽湿地相似，包括对水力和水深的控制、入口/出口结构的清洁、护堤上的除草、护堤完整性的检查、湿地植被的管理，蚊子和病媒控制（如有必要），以及常规监测。

The water depth in the wetland may need adjustment on a seasonal basis or in response to increased resistance from the accumulating plant litter in the wetland channel. Mosquitoes may require control, depending on local conditions and requirements.   The mosquito population in the treatment wetland should be no greater than in adjacent natural wetlands.

湿地中的水深可能需要在季节性基础上进行周期性调整，或者与因湿地中水流通道中累积的垃圾增加的阻力进行联动调整。蚊虫也可能需要控制，这取决于当地的条件和要求。污水处理用的FWS湿地中的蚊虫数量不应超过邻近的自然湿地。

Vegetation management in FWS wetlands does not include the routine harvest and removal of the harvested material.   Plant uptake of pollutants represents a relatively minor pathway, so harvest and removal on a routine basis does not provide a significant treatment benefit. Removal of accumulated litter may become necessary if there are severe restrictions to flow.  Generally, this will only occur if the wetland channels have been constructed    with    very    high    aspect    ratios (L:W > 10:1).  Vegetation management may also include wildlife management, depending on the type of vegetation selected for the system. Animals such as nutria and muskrats have been known to consume all emergent vegetation in FWS constructed wetlands.

FWS湿地的植被管理不包括常规收割和清除收割后的废弃物，植物本身对污染物的吸收作用只是一个相对较小的渠道，因此常规的植物收割并不能提供显著的处理效益。如果这些垃圾已经严重阻碍了水流，那可以对垃圾进行清除，一般来说，只有在湿地渠道的长宽比非常大（长∶宽>10∶1）的情况下才会发生。植被管理也可能需要对野生动物进行管理，这取决于为系统选择的植被类型。已知的动物，海狸鼠和麝鼠等动物会吃掉人工湿地中所有的挺水植物。

Routine water quality monitoring is required for all FWS systems with an NPDES permit.  The permit specifies the monitoring requirements and frequency of monitoring. Sampling for NPDES monitoring is usually limited to untreated wastewater and the final system effluent.  Since the wetland component is usually preceded by some form of preliminary treatment, the routine monitoring program does not document wetland influent characteristics. Periodic samples of the wetland influent should be obtained and tested for all but the smallest systems to provide the operator with an understanding of wetland performance and a basis for adjustments, if necessary.

所有具有NPDES许可证的SF湿地系统都需要进行常规水质监测，授权的许可将规定需要监测的污染物和频率。NPDES监测的取样通常仅限于未处理的污水和最终的系统出水。由于湿地系统通常会先进行某种形式的预处理，因此NPDES的监测并不针对具体流入湿地时的污水情况。建议在除最小系统外的所有系统中，除NPDES要求外，还应定期采集湿地进水样本并进行水质检测。这将使操作员更好地了解湿地性能，并在必要时提供调整依据。

The major items included in the capital costs for FWS wetlands are similar to those for lagoon systems, including land, site investigation, site clearing, earthwork, liner, rooting media, plants, inlet and outlet structures, fencing, miscellaneous piping, engineering, legal, contingencies, and contractor’s overhead and profit.  The liner can be the most expensive item.  For example, a plastic membrane liner can approach 40 percent of construction costs.  In many cases, compaction of the in-situ native soils provides a sufficient barrier for groundwater contamination. Table 4 summarizes capital and O&M costs for a hypothetical 378,500 liters per day (100,000 gallon per day) FWS constructed wetland, required to achieve a 2 mg/L ammonia concentration in the effluent. Other calculation assumptions include the following: influent NH3  = 25 mg/L; water temperature = 20°C   (68°F); water depth = 0.46 meters (1.5 ft); porosity = 0.75; treatment area = 1.3 hectares (3.2 ac); and land cost = $12,355/hectare ($5,000/ac).

FWS湿地的投资成本中包含的主要项目与沼泽湿地系统所需的许多项目类似，包括土地、场地调查、场地清理、土方工程、衬垫、生根介质、植物、入口和出口结构、围栏、杂项管道、工程、法律、意外开支以及承包商的间接费用和利润。衬垫可能是花费最多的项目，例如，塑料膜衬垫可以接近建筑成本的40%。在许多情况下，原生土壤的压实为地下水污染提供了足够的屏障。表4概述了一个假设的378500升/天（100000加仑/天）的FWS建造的湿地的资本和运行和维护成本，要求出水的氨浓度达到2毫克/升。其他计算假设条件包括：进水NH3=25毫克/升；水温=20℃（68℉）；水深=0.46米（1.5英尺）；孔隙率=0.75；处理面积=1.3公顷（3.2英亩）；土地成本=12,355美元/公顷（5,000美元/英亩）。

Table 5 compares the life cycle costs for this wetland to the cost of a conventional sequencing batch reactor (SBR) treatment system designed for the same flow and effluent water quality.

表5比较了该湿地的生命周期成本和为相同流量和出水水质设计的传统序批式反应器（SBR）处理系统的成本。