给排水毕设污水方向英文文献(共14页).doc

精选优质文档-倾情为你奉上 本科毕业设计外文文献及译文院 （部）：环境与化学工程学院专 业： 给水排水工程班 级： 09级02班姓 名： 许鑫学 号：翻译日期： 2013.4.16 Sewage treatmentAbstract：Sewage treatment, or domestic wastewater treatment, is the process of removing from and household sewage, both () 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 ) and a solid waste or sludge suitable for discharge or reuse back into the environment. This material is often inadvertently contaminated with many organic and inorganic compounds.Key words: Sewage treatment, fixed-film and suspended-growth, Origins of sewageSewage is created by residences, institutions, and commercial and industrial establishments. Raw influent (sewage) includes liquid from , , , , , and so forth that is disposed of via . In many areas, sewage also includes liquid waste from industry and commerce. The separation and draining of household waste into and 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 runoff. Sewage systems capable of handling stormwater are known as combined systems or . 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 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 particles and other , , , animal waste, and and . Some require stormwater to receive some level of treatment before being discharged directly into waterways. Examples of treatment processes used for stormwater include sedimentation basins, , buried concrete vaults with various kinds of filters, and vortex separators (to remove coarse solids).Process overviewSewage can be treated close to where it is created (in , or ), or collected and transported via a network of pipes and pump stations to a municipal treatment plant (see and ). 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 ).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 , 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 ) prior to discharge into a , , , or , or it can be used for the of a golf course, green way or park. If it is sufficiently clean, it can also be used for or agricultural purposes.Pre-treatmentPre-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).ScreeningThe 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 removalPre-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 treatmentIn 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 .Secondary treatmentSecondary 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 require both and a substrate on which to live. There are a number of ways in which this is done. In all these methods, the and consume biodegradable soluble organic contaminants (e.g. , fats, organic short-chain carbon molecules, etc.) and bind much of the less soluble fractions into . Secondary treatment systems are classified asfixed-film and suspended-growth. Fixed-film OR attached growth system treatment process including and 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. 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 sludgeMain article: 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 to and and ultimately to gas, (see also ). Surface-aerated basinsMost 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 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 /. 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: In older plants and plants receiving more variable loads, beds are used where the settled sewage liquor is spread onto the surface of a deep bed made up of (carbonized coal), 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 medias surfaces and eat or otherwise reduce the organic content. This 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 filtersBiological Aerated (or Anoxic) Filter (BAF) or Biofilters combine filtration with biological carbon reduction, or denitrification. BAF usually includes a reactor filled with a 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 mode. BAF is operated either in upflow or downflow configuration depending on design specified by manufacturer.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 (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 8,00012,000 mg/L, while CAS are operated in the range of 2,0003,000 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 sedimentationThe 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 contactorsMain article: 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 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 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 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