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院 （部）：环境与化学工程学院专 业：班 级：姓 名：学 号：翻译日期：
给水排水工程 09级02班 许鑫
*********** 2013.4.16
Sewage treatment
Abstract：Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff (effluents) and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants. Its objective is to produce a waste stream (or treated effluent) and a solid waste or sludge suitable for discharge or reuse back into the environment. This material is often inadvertently contaminated with many toxic organic and inorganic compounds.
Key words: Sewage treatment, fixed-film and suspended-growth, Activated sludge
Origins of sewage
Sewage is created by residences, institutions, and commercial and industrial establishments. Raw influent (sewage) includes household waste liquid from toilets, baths, showers, kitchens, sinks, and so forth that is disposed of via sewers. In many areas, sewage also includes liquid waste from industry and commerce. The separation and draining of household waste into greywater and blackwater is becoming more common in the developed world, with greywater being permitted to be used for watering plants or recycled for flushing toilets. A lot of sewage also includes some surface water from roofs or hard-standing areas. Municipal wastewater therefore includes residential, commercial, and industrial liquid waste discharges, and may include stormwater runoff. Sewage systems capable of handling stormwater are known as combined systems or combined sewers. Such systems are usually avoided since they complicate and thereby reduce the efficiency of sewage treatment plants owing to their seasonality. The variability in flow also leads to often larger than necessary, and subsequently more expensive, treatment facilities. In addition, heavy storms that contribute more flows than the treatment plant can handle may overwhelm the sewage treatment system, causing a spill or overflow. It is preferable to have a separate storm drain system for stormwater in areas that are developed with sewer systems.
As rainfall runs over the surface of roofs and the ground, it may pick up various contaminants including soil particles and other sediment, heavy metals, organic compounds, animal waste, and oil and grease. Some jurisdictions require stormwater to receive some level of treatment before being discharged directly into waterways. Examples of treatment processes used for stormwater include sedimentation basins, wetlands, buried concrete vaults with various kinds of filters, and vortex separators (to remove coarse solids).
Process overview
Sewage can be treated close to where it is created (in septic tanks, biofilters or aerobic treatment systems), or collected and transported via a network of pipes and pump stations to a municipal treatment plant (see sewerage and pipes and
infrastructure). Sewage collection and treatment is typically subject to local, state and federal regulations and standards. Industrial sources of wastewater often require specialized treatment processes (see Industrial wastewater treatment).
Conventional sewage treatment may involve three stages, called primary, secondary and tertiary treatment. Primary treatment consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface. The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment. Secondary treatment removes dissolved and suspended biological matter. Secondary treatment is typically performed by indigenous, water-borne
micro-organisms in a managed habitat. Secondary treatment may require a separation process to remove the micro-organisms from the treated water prior to discharge or tertiary treatment. Tertiary treatment is sometimes defined as anything more than primary and secondary treatment. Treated water is sometimes disinfected chemically or physically (for example by lagoons and microfiltration) prior to discharge into a stream, river, bay, lagoon or wetland, or it can be used for the irrigation of a golf course, green way or park. If it is sufficiently clean, it can also be used for groundwater recharge or agricultural purposes.
Pre-treatment
Pre-treatment removes materials that can be easily collected from the raw wastewater before they damage or clog the pumps and skimmers of primary treatment clarifiers (trash, tree limbs, leaves, etc).
Screening
The influent sewage water is strained to remove all large objects carried in the sewage stream. This is most commonly done with an automated mechanically raked bar screen in modern plants serving large populations, whilst in smaller or less modern plants a manually cleaned screen may be used. The raking action of a mechanical bar screen is typically paced according to the accumulation on the bar screens and/or flow rate. The solids are collected and later disposed in a landfill or incinerated.
Grit removal
Pre-treatment may include a sand or grit channel or chamber where the velocity of the incoming wastewater is carefully controlled to allow sand, grit and stones to settle.
Primary treatment
In the primary sedimentation stage, sewage flows through large tanks, commonly called \"primary clarifiers\" or \"primary sedimentation tanks\". The tanks are large enough that sludge can settle and floating material such as grease and oils can rise to the surface and be skimmed off. The main purpose of the primary sedimentation stage is to produce both a generally homogeneous liquid capable of being treated biologically and a sludge that can be separately treated or processed. Primary settling tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank from where it can be pumped to further sludge treatment stages. Grease and oil from the floating material can sometimes be recovered for saponification.
Secondary treatment
Secondary treatment is designed to substantially degrade the biological content of the sewage which are derived from human waste, food waste, soaps and detergent.
The majority of municipal plants treat the settled sewage liquor using aerobic biological processes. For this to be effective, the biota require both oxygen and a substrate on which to live. There are a number of ways in which this is done. In all these methods, the bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugars, fats, organic short-chain carbon molecules, etc.) and bind much of the less soluble fractions into floc. Secondary treatment systems are classified as
fixed-film and suspended-growth.
Fixed-film OR attached growth system treatment process including trickling filter and rotating biological contactors where the biomass grows on media and the sewage passes over its surface.
In suspended-growth systems, such as activated sludge, the biomass is well mixed with the sewage and can be operated in a smaller space than fixed-film systems that treat the same amount of water. However, fixed-film systems are more able to cope with drastic changes in the amount of biological material and can provide higher removal rates for organic material and suspended solids than suspended growth systems.
Roughing filters are intended to treat particularly strong or variable organic loads, typically industrial, to allow them to then be treated by conventional secondary treatment processes. Characteristics include typically tall, circular filters filled with open synthetic filter media to which wastewater is applied at a relatively high rate. They are designed to allow high hydraulic loading and a high flow-through of air. On larger installations, air is forced through the media using blowers. The resultant wastewater is usually within the normal range for conventional treatment processes.
Activated sludge
Main article: Activated sludge
In general, activated sludge plants encompass a variety of mechanisms and processes that use dissolved oxygen to promote the growth of biological floc that substantially removes organic material.
The process traps particulate material and can, under ideal conditions, convert ammonia to nitrite and nitrate and ultimately to nitrogen gas, (see also denitrification).
Surface-aerated basins
Most biological oxidation processes for treating industrial wastewaters have in common the use of oxygen (or air) and microbial action. Surface-aerated basins achieve 80 to 90% removal of Biochemical Oxygen Demand with retention times of 1 to 10 days. The basins may range in depth from 1.5 to 5.0 metres and use motor-driven aerators floating on the surface of the wastewater.
In an aerated basin system, the aerators provide two functions: they transfer air into the basins required by the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes). Typically, the floating surface aerators are rated to deliver the amount of air equivalent to 1.8 to 2.7 kg O2/kW·h. However, they do not provide as good mixing as is normally achieved in activated sludge systems and therefore aerated basins do not achieve the same performance level as activated sludge units.
Biological oxidation processes are sensitive to temperature and, between 0 °C and 40 °C, the rate of biological reactions increase with temperature. Most surface aerated vessels operate at between 4 °C and 32 °C.
Filter beds (oxidizing beds)
Main article: Trickling filter
In older plants and plants receiving more variable loads, trickling filter beds are used where the settled sewage liquor is spread onto the surface of a deep bed made up of coke (carbonized coal), limestone chips or specially fabricated plastic media. Such media must have high surface areas to support the biofilms that form. The liquor is distributed through perforated rotating arms radiating from a central pivot. The distributed liquor trickles through this bed and is collected in drains at the base. These drains also provide a source of air which percolates up through the bed, keeping it aerobic. Biological films of bacteria, protozoa and fungi form on the media’s surfaces
and eat or otherwise reduce the organic content. This biofilm is grazed by insect larvae and worms which help maintain an optimal thickness. Overloading of beds increases the thickness of the film leading to clogging of the filter media and ponding on the surface.
Biological aerated filters
Biological Aerated (or Anoxic) Filter (BAF) or Biofilters combine filtration with biological carbon reduction, nitrification or denitrification. BAF usually includes a reactor filled with a filter media. The media is either in suspension or supported by a gravel layer at the foot of the filter. The dual purpose of this media is to support highly active biomass that is attached to it and to filter suspended solids. Carbon reduction and ammonia conversion occurs in aerobic mode and sometime achieved in a single reactor while nitrate conversion occurs in anoxic mode. BAF is operated either in upflow or downflow configuration depending on design specified by manufacturer.
Membrane bioreactors
Membrane bioreactors (MBR) combine activated sludge treatment with a membrane liquid-solid separation process. The membrane component uses low pressure microfiltration or ultra filtration membranes and eliminates the need for clarification and tertiary filtration. The membranes are typically immersed in the aeration tank; however, some applications utilize a separate membrane tank. One of the key benefits of an MBR system is that it effectively overcomes the limitations associated with poor settling of sludge in conventional activated sludge (CAS) processes. The technology permits bioreactor operation with considerably higher mixed liquor suspended solids (MLSS) concentration than CAS systems, which are limited by sludge settling. The process is typically operated at MLSS in the range of 8,000–12,000 mg/L, while CAS are operated in the range of 2,000–3,000 mg/L. The elevated biomass concentration in the MBR process allows for very effective removal of both soluble and particulate biodegradable materials at higher loading rates. Thus increased Sludge Retention Times (SRTs) — usually exceeding 15 days — ensure complete nitrification even in extremely cold weather.
The cost of building and operating an MBR is usually higher than conventional wastewater treatment. Membrane filters can be blinded with grease or abraded by suspended grit and lack a clarifier's flexibility to pass peak flows. The technology has become increasingly popular for reliably pretreated waste streams and has gained wider acceptance where infiltration and inflow have been controlled, however, and the life-cycle costs have been steadily decreasing. The small footprint of MBR systems, and the high quality effluent produced, make them particularly useful for water reuse applications.
There are MBR plants being built throughout the world, including North Librty, Iowa, Georgia, and Canada.
Secondary sedimentation
The final step in the secondary treatment stage is to settle out the biological floc or filter material and produce sewage water containing very low levels of organic material and suspended matter.
Rotating biological contactors
Main article: Rotating biological contactor
Rotating biological contactors (RBCs) are mechanical secondary treatment systems, which are robust and capable of withstanding surges in organic load. RBCs were first installed in Germany in 1960 and have since been developed and refined into a reliable operating unit. The rotating disks support the growth of bacteria and micro-organisms present in the sewage, which breakdown and stabilise organic pollutants. To be successful, micro-organisms need both oxygen to live and food to grow. Oxygen is obtained from the atmosphere as the disks rotate. As the
micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage. Effluent from the RBC is then passed through final clarifiers where the micro-organisms in suspension settle as a sludge. The sludge is withdrawn from the clarifier for further treatment.
A functionally similar biological filtering system has become popular as part of home aquarium filtration and purification. The aquarium water is drawn up out of the tank and then cascaded over a freely spinning corrugated fiber-mesh wheel before
passing through a media filter and back into the aquarium. The spinning mesh wheel develops a biofilm coating of microorganisms that feed on the suspended wastes in the aquarium water and are also exposed to the atmosphere as the wheel rotates. This is especially good at removing waste urea and ammonia urinated into the aquarium water by the fish and other animals.
污水处理
摘要
自然或生活污水处理，是指清除包括家庭排放的和地面径流在内的污水废水和地面污染物的过程。它包括物理，化学和生物过程，消除物理，化学和生物污染物。其目的是集中产生废物流（或经处理的污水）以及固体废物或污泥进行处理或再进入环境。这种污物通常是在无意中受到了许多有毒的有机和无机物的污染。
关键词：污水处理，生物膜处理法和停止增长生物处理法，活性污泥法，
污水起源
污水是由个人住宅，机关，商业和工业机构产生的。原进水（污水）包括家庭的厕所，浴室，淋浴，厨房，水槽废液等等，这些水将通过污水管排放。在许多地区，污水也包括工业和商业污水。在发达国家，家居分别将污水排放为灰水和黑水已经越来越普遍，因为灰水可以用于浇灌植物或回收用来冲马桶。大量的污水还包括一些屋顶流下的水以及地表水。因此城市废水包括住宅，商业和工业排放的废水，且可能包括雨水径流。具有处理雨水能力的污水处理系统被称为合流排水系统。这种系统通常是不被普遍采用，因为它们复杂化而且由于其季节性，降低了污水处理厂的效率。由于流量的经常变化，也导致处理量往往大于必需的，因而使处理设施更昂贵。此外，当遭遇暴雨时，过量的雨水会造成污水处理能力不足，因而引发溢流。因此在设计排水管网时最好采用雨污分流系统。
由于降雨流经屋顶和地面时，会带走包括土壤颗粒和其他沉积物，重金属，有机物，动物排泄物，污油和油脂等各种污染物质。因此有些地方会有法律要求在雨水排入河道之前要进行一些一定水平的处理。例如以下对雨水进行的处理：盆地沉淀处理，湿地过滤处理，混凝土地窖过滤处理，和旋涡分离器（去除粗固体）。
过程概述
污水可以在下列构筑物(化粪池，生物过滤器或好氧处理系统）附近被处理，或收集并通过排水管网和泵站送至城市污水处理厂（见污水处理和管道和基础设施）。污水收集和处理，通常取决于当地州和联邦法规和标准。来源于的工业废水，往往需要专门的处理过程（见工业废水处理）。
常规污水处理可能涉及三个阶段，一级处理，二级处理和三级处理。一级处理包括在沉淀池中的短时停留，这样比较重的固体就会沉到池底，而油，油脂，
更轻的固体则浮到水面。沉淀的和浮动的材料都将被去除，其余的液体可被释放或继续二级处理。二级处理可以去除溶解和悬浮的生物物质。二级处理通常由好氧或厌氧微生物进行。二级处理还可能需要一个分离过程，以去除残余的微生物或进行三级处理。三级处理有时被界定为与一级和二级不同的过程。受处理的水在排放到河流，海湾，泻湖或湿地前有时需要化学消毒或物理（例如泻湖和微滤）处理，或者可以用于灌溉高尔夫球场，绿色道路或公园。如果它足够清洁，也可以用于地下水回灌或农业用途。
预处理
预处理可以从原始废水除去垃圾，树枝，树叶等比较容易收集的物质，以防止其损坏或阻塞水泵和一级处理的澄清池处理。
筛选
进水污水必须消除随污水流进行的大的污染物。在服务大量人口的现代化处理厂，经常用自动倾斜格栅来达到这个目的。而小的处理厂可能采用手动的格栅。机械式格栅的清污是典型的以格栅污物积累或流量的积累来进行的。收集到的固体将被进行填埋或焚烧处理。
除砂
预处理可使包括沙子或砂砾在内的物质通过控制速度在渠道或厅室内旋转流动，使砂，砂砾和石块沉淀。
初级处理
在初级沉淀阶段，污水流经一个大池子，俗称“初级澄清池”或“初级沉淀池”。这些池子需要足够大以令污泥可以沉淀而油和油脂等漂浮物可以上升到表面，并掠出池子。在初级沉淀阶段的主要目的是提供一个均匀的液态环境使微生物和污泥都能被处理。初级沉淀池，通常装配有机械驱动的刮削泥器，不断推动将污泥收集到底部污泥斗，从那里可以抽取污泥进行进一步处理。油脂和石油的漂浮物有时会回收进行皂化。
二级处理
二级处理的设计是为了降低了污水中那些来自人类垃圾，食物渣滓，肥皂和洗涤剂产生的生化生物污染。大多数市政都打算采用好氧生物的方法解决污水处理问题。为了达到这个目的，生物既需要的氧也需要生活的底物。有多种方式来达到这个目的。在所有这些方法中，细菌和原生动物生物都可以降解消耗水中的
水溶性有机污染物（如糖，脂肪，有机短链碳分子等），将大部分可溶性组分结合成絮状。二级处理系统被分为
生物膜处理法和停止增长生物处理法。
生物膜处理法和停止增长生物处理法系统的处理流程包括生物滤池和生物转盘，它们提供生物生长的媒体以使污水流过时进行处理。
在停止增长生物处理法如活性污泥系统中，生物质可以与与污水充分混合，而且在处理等量污水时可以比膜系统采用更小的空间操作。然而，生物膜系统比停止增长生物处理法更能够应付生物污染物数量急的剧变化，并能提供更高的有机物及悬浮固体去除率。
粗过滤器是为了处理特别强烈的或可变有机负荷，一般工业，允许它们由传统的二级处理工艺处理后在进行处理。在废水处理程度要求较高的地方，典型的特征包括高及包含开放合成过滤介质的圆形填充过滤器。它们的目的是允许通过高负荷的水力和高速流动的空气。在较大的装置中，使用鼓风机以使空气强行通过装置。由此产生的废水通常在常规处理工艺的正常范围内。
活性污泥法 主条目：活性污泥
一般来说，生物活性污泥法涵盖的各种机制和方法，通过溶解氧，以促进生物絮体增长，以此极大地消除有机物质的。
这个过程中的颗粒物质在理想的条件下，可将氨转化为亚硝酸盐和硝酸盐，并最终为氮气（另见反硝化）。
表面曝气池
大部分工业废水处理的生物氧化过程对氧气（或空气）和微生物的利用是相同的。表面曝气池在一到十天的停留时间内，对生化需氧量的去除可达到80%至90％。曝气池的深度为1.5至5.0米之间，使用电机驱动对废水水面进行曝气的。
在一个曝气池系统中，曝气机提供两个功能：他们转移生物氧化反应所需要的空气至曝气池，它们提供空气的分散和反应物的接触的所需（即，氧气，污水和微生物） 。通常情况下，浮动表面曝气机的额定供气量，相当于1.8 至2.7公斤氧气/千瓦•每小时。然而，在活性污泥系统中，它们并不能保证提供混合达到预定值，因此活性污泥系统中的曝气池也不一定能达到预定的水平。
生物氧化过程对温度敏感，并在0 ° C和40 ° C时，生物反应速度随温度的
上升而上升。大多数表面曝气池运行温度为4 ° C至32 ° C。
滤池（氧化沟） 主条目：滤池
在老厂和负荷变化较大的处理厂中，滤池被用来解决在焦碳（碳化煤），灰石芯片或专门制造的各种塑料介质上漫流的污水溶液。这种介质必须有足够的表面积以支持生物膜的形成。这种溶液是由中心枢纽发出，通过旋臂上的穿孔扩散的。扩散的溶液穿过滤池，并在池底通过管道被收集。这些管道同时也让空气进入滤池，以保持其氧气的充足。分布在介质表面的细菌，原生动物和真菌生物将以消化或以其他方式使有机质含量减少。幼虫和蠕虫将使生物膜消耗，以帮助维持生物膜最佳的厚度。因为生物膜过厚将会导致介质堵塞和滤池上表面积水。
曝气生物过滤器
曝气生物滤池（或缺氧）滤池（BAF）或生物滤池，将生物还原碳过滤和硝化反硝化过滤结合在了一起。曝气生物滤池通常包括一个由过滤介质填充的反应器。这个滤料是悬浮的或者是由过滤池底的砾石层支撑的。这个介质的两个目的是支持存在于它上面的微生物的高活性和过滤悬浮固体。在有氧模式下进行碳减排和氨的转化，缺氧模式下只进行单一的硝酸转化。曝气生物滤池的运作是上流还是下流要取决于设计制造商设计及说明。
膜生物反应器
膜生物反应器（MBR）将活性污泥法和膜的固液分离结合到了一起。膜是由低压微滤或超滤膜组成的，因此不必再进行澄清或第三次过滤。膜通常是沉浸在曝气池中的，然而，也有一些是单独应用一个膜反应池的。对一个MBR系统的主要好处之一是，它有效地克服了传统活性污泥工艺中的污泥的沉降差问题。与CAS系统相比，该技术允许反应器在具有相当高浓度的混合液悬浮固体的情况下操作，而这是由污泥沉淀物决定的。这一反应过程通常是在混合液悬浮固体颗粒浓度为8,000-12,000毫克/升中进行的，而CAS的允许操作范围为2000-3000毫克/升。MBR过程中生物量浓度的升高，可以非常有效地将可溶性颗粒和负荷率较高的生物可降解材料去除。因此，增加污泥滞留时间（SRTs） - 通常超过15天 – 即可确保即使在极其寒冷的天气里也能完全硝化。
建设和经营一个MBR的成本通常高于传统的废水处理。膜过滤器会被油污堵塞或被水流中的沙粒摩擦刮破，且缺乏洪峰流量通过时净水的灵活性。这项技术在可靠的预处理废水上已日益普遍，并取得了广泛的接受，而且流入水源也已
受到控制，同时，生命周期成本一直在稳步下降。膜生物反应器系统的体积小，且可以高质量的处理污水，使他们在中水回用方面大受欢迎。
膜生物反应器在世界各地都有建立。包括北Librty，爱荷华，格鲁吉亚和加拿大。
二次沉淀
在第二阶段处理的最后一步是为了使生物絮凝或过滤材料沉淀和产出含有有机物质及悬浮物含量极低的污水。
生物转盘
主条目：旋转生物接触池
旋转生物接触池（RBCs）是机械二级处理系统，在承受激增的有机负荷时有强大的应该变能力。旋转生物接触池于1960年在德国第一次安装，至今已发展完善成为一种可靠的处理工序。转盘为污水中的细菌和微生物提供生长方面的支持，用来破坏与稳定有机污染物。要取得成功，就要提供微生物生活所需的氧气和生长所需的食物。氧气是转盘旋转过程中从大气中获得的。当微生物成长时，它们建立于转盘介质之上，直到它们被污水中转盘旋转产生的剪切力所甩开。从旋转生物接触池流出的污水，将通过最后澄清池在那里悬浮的微生物将沉淀为絮状物。澄清池中的污泥将被分离进行进一步处理。
与其功能类似的生物过滤系统已成为家庭鱼缸受欢迎的过滤和净化的一部分。该过滤系统被设计为水先流出池子，之后瀑布般自由流经一个皱褶的纤维网格转轮，之后在穿过一个含有介质的过滤器，然后流回鱼缸。纱网转轮将成为一个以水族箱中悬浮饲料废物为食的微生物形成的生物膜，同时转轮也由于旋转而暴露于大气。这个系统尤其是善于消除鱼类和其他动物通过排泄而在水中产生的尿素和浪费尿素和氨。
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