給排水專業(yè)英語_英文1

1、sewage treatmentthe objective of sewage treatment is togproduce a disposable effluent without causing harm or trouble to the communities and prevent pollution sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff

2、 (effluents) and domestic 1( 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 ma

3、terial is often inadvertently contaminated with many toxic organic and inorganic compounds.origins of sewagesewage is created by residences, institutions, and commercial and industrial establishments. raw influent (sewage) includes household waste liquid from toilets, baths, showers, kitchens, sinks

4、, and so forth that is disposed of via sewers in many areas, sewage also in eludes 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 wateri

5、ng 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 in elude stormwater runoff. sewage systems capable of handl

6、ing 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 exp

7、ensive, treatment facilities. in addition, heavy storms that con tribute 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

8、 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 bein

9、g 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 overviewsewage can be treated close to where it is created (

10、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 an

11、d 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

12、 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 b

13、iological 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 some

14、times 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, gr

15、een way or park .if it is sufficiently clean, it can also be used for groundwater recharge or agricultural purposesprocess flow diagram for a typical large-scale treatment plantpretreatmentpre-treatmentpre-treatment removes materials that can be easily collected from the raw wastewater before they d

16、amage 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 modem plants se

17、rving 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 incin

18、erated.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 treatmentan empty sedimentation tank at the treatment plant in hlerchtem, belgium in the primary sedim

19、entation stage, sewage flows through large tanks, commonly called "primary clarifiers11 or "primary sedimentation tanks11 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 prim

20、ary 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

21、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 treatmentsecondary treatment is designed to substantially degrade the biological content of the sewage wh

22、ich 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

23、 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 fixedor suspended-growth.fixe

24、d-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 surfacein suspended-growth systems, such as activated sludge, the biomass is well mixed with the sewage and can be operated

25、 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.ro

26、ughing 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 wastewat

27、er is applied at a relatively high rate. they are designed to allow high hydraulic loading and a high flow-through of ai匚 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

28、 sludgemain article: activated sludgeraw waterclarifiei-settleraeration tankrecycle sludgeg3gotreatedwaterto sludge treatmentin general, activated sludge plants encompass a variety of mechanisms and processes that use dissolved oxygen to promote the growth of biological floc that substantially remov

29、es organic materialthe process traps particulate material and can, under ideal conditions, convert ammonia to nitrite and nitrate and ultimately to nitrogen gas, (see also denitrification).a generalized, schematic diagram of an activated sludge q process.surface-aerated basinselectric motor with pro

30、peller and slinger-ring on vertical motor shafta typical surface - aerated basinnote: the ring floats are tethered to posts on the berms.a typical surface-aerated basin (using motor-driven floating 匸1 aerators)most biological oxidation processes for treating industrial wastewaters have in common the

31、 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 wastewaterin an aerated b

32、asin 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

33、aerators are rated to deliver the amount of air equivalent to 1.8 to 2.7 kg 02/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 unitsbiological oxidation pro

34、cesses 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 °cfilter beds (oxidizing beds)main article: trickling filterin older plants and plants receivin

35、g 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 liqu

36、or 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,

37、 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

38、 on the surface.biological aerated filtersbiological 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 gr

39、avel 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

40、anoxic mode baf is operated either in upflow or down flow configuration depending on design specified by manufacturer.membrane bioreactorsmembrane bioreactors (mbr) combine activated sludge treatment with a membrane liquid-solid separation process. the membrane component uses low pressure microfiltr

41、ation 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 lank. one of the key benefits of an mbr system is that it effectively overcomes the

42、 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 typica

43、lly operated at mlss in the range of &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

44、sludge retention times (srts) 一 usually exceeding 15 days 一 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 la

45、ck a clarifiefs flexibility to pass peak flows. the technology has become increasingly popular forseconciary sedimentation tank at a ruralqtreatment plant.reliably pretreated waste streams and has gained wider acceptance where infiltration and inflow have been controlled, however, and the life-cycle

46、 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 canadasecondary sedimentationt

47、he 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 contactorschematic diagram of a typical rotating biological contactor (rbc)