外文翻譯污水的生物處理過程

1、附錄：wastewater biological treatment processesthe objective of wastewater treatment is to reduce the concentration of specific pollutants to the level at which the discharge of the effluent will not adversely affect the environment or pose a health threat. moreover , reduction of these constituents ne

2、ed only be to some required level.for any given wastewater in a specific location , the degree and type of treatment are variables that require engineering decisions . often the degree of treatment depends on the assimilative capacity of the receiving water . do sag curves can indicate how much bod

3、must be removed from wastewater so that the do of receiving water is not depressed too far . the amount of bod that must be removed is an effluent standard and dictates in large part the type of wastewater treatment required .to facilitate the discussion of wastewater , assume a “ typical wastewater

4、 ”and assume further that the effluent from this wastewater treatment must meet the following effluent standards :bod15mg/lss15mg/lp1mg/ladditional effluent standard could have been established , but for illustrative purposes we consider only these three . the treatment system selected to achieve th

5、ese effluent standards includes 1. primary treatment : physical processes that nonhomogenizable solids and homogenize the remaining effluent .2. secondary treatment : biological process that remove most of the biochemical demand for oxyen .3. tertiary treatment : physical , biological , and chemical

6、 processes to remove nutrients like phosphorus and inorganic pollutants , to deodorize and decolorize effluent water , and to carry out further oxidation .primary treatment the most objectionable aspect of discharging raw sewage into watercourses is the floating material . thus screen were the first

7、 form of wastewater treatment used by communities , and they are used today as the first step in treatment plants .typical screens consist of a series bars that might be about 2.5 cm apart . a screen in a modern treatment plant removes might damage equipment or hinder further treatment . in some old

8、er treatment plants are cleaned by hand , but mechanical cleaning equipment is used in almost all new plants . the cleaning rakes are activated when screens get sufficiently clogged to raise the water level in front of the bars .in many plants , the second treatment step is a comminutor , a circular

9、 grinder designed to grind the solids coming through the screen into pieces about 0.3 cm or less in diameter .the third treatment step is the removal of grit or sand from the wastewater . grit and sand can damage equipment like pumps and flow meters and must be removed . the most common grit chamber

10、 is a wide place in the channel where the flow is slowed enough to allow the dense grit to settle out . sand is about 2.5 times dense than most organic solids and thus settles much faster . the objective of a grit chamber is to remove sang and grit without removing organic material .organic material

11、 must be treated further in the plant , but the separated sand may be used as fill without additional treatment .most wastewater treatment plants have a settling tank after the grit chamber , to settle out as much material as possible . accordingly , the retention time is long and turbulence is kept

12、 to a minimum .the solids settle to the bottom of the tank and are removed though a pipe , while the clarified liquid escapes over a v-notch weir that distributes the liquid discharge equally all the way around a tank . settling tanks are also called sedimentation tank or clarifiers . the settling t

13、ank that immediately follows screening and grit removal is called the primary clarifier . the solids that drop to the bottom of a primary clarifier are removed as raw sludge .raw sludge generally has a powerfully unpleasant odor , is full of pathogenic , and is wet , three characteristics that make

14、its disposal difficult . it must be stabilized to retard further decomposition and dewatered for ease of disposal .the objective of primary treatment is the removal of solids , although some bod is removed as a consequence of the removal of decomposable solids .a substantial fraction of the solids h

15、as been removed , as well as some bod is a little p , as a consequence of the removal of raw sludge . after primary treatment the wastewater may move on to secondary treatment .secondary treatmentwater leaving the primary clarifier has not lose much of the solid organic matter but still contains hig

16、h-energy molecules that decompose by microbial action , creating bod . the demand for oxygen must be reduce (energy wasted ) or else the discharge may create unacceptable condition in the receiving waters . the objective of secondary treatment is to remove bod , where the objective of primary treatm

17、ent is to remove solids .the trickling filter consists of a filter bed of fist-sized rocks or corrugated plastic blocks over which the waste is trickled . the name is something of a misnomer since no filtration takes place . a very active biological growth forms on the rocks , and these organisms ob

18、tain their food from the waste stream dipping through the rock bed . air either is forced through the rocks or circulates automatically because of the difference between the air temperature in the bed and ambient temperatures . trickling filters use a rotating arm that moves under its own power , li

19、ke a lawn sprinkler , distributing the waste evenly over the entire bed . often the flow is recirculated and a higher degree of treatment attained .trickling filtration was a well-established treatment system at the beginning of the twentieth century . in 1914 , a pilot plant was built for a differe

20、nt system that bubbled air through free-floating aerobic microorganisms , a process which became known as the activated sludge system . the activated sludge process differs from trickling filtration in that the microorganisms are suspended in the liquid .an activated sludge system includes a tank fu

21、ll of waste liquid from the primary clarifier and a mass of microorganisms . air bubbled into this aeration tank provides the necessary oxygen for survival of the aerobic organisms . the microorganisms come in contact with dissolved organic matter in the wastewater . adsorb this material , and ultim

22、ately decompose the organic material to co2 , ho2 ,some stable compounds , and more microorganisms .when most of the organic material , that is , food for the microorganisms , has been used up , the microorganisms are separated from the liquid in a settling tank , sometimes called a secondary or cla

23、rifier . the microorganisms remaining in the settling tank have no food available , become hungry , and are thus activated-hence the term activated sludge . the clarified liquid escapes over a weir and may be discharged into the receiving water . the settle microorganisms , now called return activat

24、ed sludge , are pumped back to the head of the aeration tank , where they find more food in the organic compounds in the liquid entering the aeration tank from the primary clarifier , and the process starts over again . activated sludge treatment is a continuous process ,with continuous sludge pumpi

25、ng and clean-water discharge .activated sludge treatment produces more microorganisms than necessary and if the microorganisms are not removed , their concentration will soon increase and clog the system with solids . some of the microorganisms must therefore be wasted and the disposal of such waste

26、 activated sludge in one of the most difficult aspects of wastewater treatment .activated sludge system are designed on the basis of loading , or the amount of organic matter , or food , added relative to the microorganisms available . the food-to-microorganisms (f/m) ratio is major design parameter

27、 . both f and m are difficult to measure accurately , but may be approximated by influent bod and ss in the aeration tank , respectively . the combination of liquid and microorganisms undergoing aeration is known as mixed liquor , and the ss in the aeration tank are mixed liquid suspended solids (ml

28、ss) . the ratio of influent bod to mlss , the f/m ratio , is the loading on the system , calculated as pounds (or kg ) of bod per day per pound or kg of mlss .relatively small f/m ,or little food for many microorganisms , and a long aeration period (long retention time in the tank ) result in a high

29、 degree of treatment because the microorganisms can make maximum use of available food . systems with these features are called extended aeration systems and are widely used to treat isolated wastewater source , like small developments or resort hotels . extended aeration systems create little exces

30、s biomass and little excess activated sludge to dispose of .the success of the activated sludge system also depends on the separation of the microorganisms in the final clarifier . when the microorganisms do not settle out as anticipated , the sludge is said to be a bulking sludge , bulking is often

31、 characterized by a biomass composed almost totally of filamentous organisms that from a king of lattice structure within the sludge floes which prevents settling . a trend toward poor settling may be the forerunner of a badly upset and ineffective system . the settle ability of activated sludge is

32、most often described by the sludge volume index (svi) , which is reasoned by allowing the sludge to settle for minutes in a 1-lcyliner . if the svi is 100 or lower , the sludge solids settle rapidly and the sludge returned to the final clarifier can be expected at a high solids concentration . svi i

33、s about 200 , however , indicate bulking sludge and can lead to poor treatment .tertiary treatment the effluent from secondary treatment meets the previously established effluent standards for bod and ss . only phosphorus content remains high . the removal of inorganic compounds , including inorgani

34、c phosphorus and nitrogen compounds , requires advanced or tertiary wastewater treatment .primary and secondary (biological) treatment are a part of conventional wastewater treatment plants . however , secondary treatment plant effluents are still significantly polluted . some bod and suspended soli

35、ds remain , and neither primary nor secondary treatment is effective in removing phosphorus and other nutrients or toxic substances . a popular advanced treatment for bod removal is the polishing pond , or oxidation pond , commonly a large lagoon into which the secondary effluent flows . such ponds

36、have a long retention time , often measured in weeks .bod may also be removed by activated carbon adsorption , which has the added advantage of removing some is a completely enclosed tube , which dirty water is pumped into bottom and clear water exits at the top . microscopic crevices in the carbon

37、catch and hold colloidal and smaller particles . as the carbon column becomes saturated , the pollutants must be removed from the carbon and the carbon reactivated , usually by heating it in the absence of oxygen . reactivated or regenerated carbon is somewhat less efficient than using virgin carbon

38、 , some of which must always be added to ensure effective performance .附錄：污水的生物處理過程物水處理的目的是降解特定污染物的濃度使其達到污水排放不影響環(huán)境或形成健康威脅的程度，而且降低這些成分僅僅需要達到要求大的水平即可。應為任何給定的污水在來源，處理程度和類型方面是變化的，而這種變化是由工業(yè)決定的，而且處理程度往往依賴接納水體的同化能力。氧垂曲線能顯示多少bod必須從污水中去除以致于使接納水體的溶解氧不致降低太多。在大部分的污水處理要求的類型中，必須被去除的bod數(shù)量是污水的一個標準和指標。為了便于討論污水，假定一種“

39、典型的污水”而且假定這種污水通過處理必須達到以下的污水標準：bod 15 mg/lss 15 mg/lp 1 mg/l增加的污水標準應該被列出，但是為了說明目的我們僅僅考慮這三項。能達到這些污水標準的處理系統(tǒng)包括：1. 初級處理：固體物質非均勻化和污水排放均勻化的物理過程。2. 二級處理：依靠氧去除大部分生化物質的生物處理過程。3. 三級處理：物理，生物和化學過程的目的就是去除營養(yǎng)物質，像磷和有機物等，而且去除污水的臭味，色度和更多的氧化物。初級處理排放原污水到水域中最厭惡的一個方面是其中的漂浮物，因此，格柵被用在社區(qū)污水處理的首要位置，現(xiàn)在它們被作為處理方案的第一步，典型的格柵由一系列的鋼條

40、組成，這些鋼條之間大約相距2.5cm，在現(xiàn)代的處理方案中，格柵攔截了那些可能對設備造成破壞或者影響后續(xù)處理的物質，在過去的一些舊的處理方案中，格柵通過人工清洗；但是現(xiàn)在幾乎所有的方案中都用機械清洗設備。當格柵被阻塞使水位上升到柵條以上時，清洗設備被啟動。在許多方案中，第二步是粉碎，循環(huán)擠壓固體物質通過格柵形成大約3.0cm或更小直徑的小塊。第三步處理是去處污水中的沙粒和石子，沙粒和石子會損壞設備，像水泵和流量計，因此必須被去除。大部分沉沙池是個很寬的空間，在這個渠道內(nèi)水流慢到足夠大密度的沙粒沉淀下來，沙粒的密度是大部分有機物密度的2.5倍，因此沉淀的比較快。沉沙池的目的就是去除沙粒和石子，而不

41、去除有機顆粒，在處理過程中有機物必須被進一步處理而分離除的出的沙?？梢员挥米魈畛湮锒鵁o需額外處理。大部分污水處理方案中在沉沙池后面都有一個沉淀池，目的就是盡可能的去除固體顆粒，因此，停留時間比較長，水流速度保持比較慢。固體沉淀到池子底部，然后通過管道被清除，而被澄清的液體則通過均勻布置在池子周圍的v型溢流堰排放，沉淀池也被稱為沉積池或澄清池，緊隨在清渣和除沙之后的沉淀池也被叫作初次澄清池，沉淀在初次澄清池底部而被排放的固體稱為原污泥。原污泥通常有很強的令人不快的氣味，含有病原有機體，而且含水率高，這三個特點增加了它處理的困難，它必須被穩(wěn)定為了防止它進一步腐化，也為了容易脫水處理。初級處理的目的

42、就是去除固體顆粒，然而一些bod也在分離固體物質的一系列過程中被去除了。相當?shù)囊徊糠止腆w物質，還有一部分bod和少量的p作為原污泥的產(chǎn)物而被去除了，被初級處理之后污水可能繼續(xù)進行二級處理。二級處理水離開初次澄清池并沒有去除多少固體有機物，而且仍含有能通過微生物作用分解的高能量分子，成為bod。要求氧必須減少，否則，在接納的水體中排放可能出現(xiàn)不能接受的情況。二級處理的目的就是去除bod，而初級處理的目的則是去除固體顆粒。慮池由拳頭大小的礫石或波紋塑料板的慮床組成，通過它污物被慮掉，命名可能有錯誤，因為根本沒有過濾發(fā)生?；钚晕⑸锔街诘[石上，空氣被強制通過礫石或自動循環(huán)，因為慮床空氣溫度和周圍溫度的差異，慮池用一個循環(huán)調(diào)節(jié)系統(tǒng)降低它的能耗，像一個均勻布水裝置，能均勻的在整個慮床上分布污水，而通常水流是循環(huán)的，因而更高程度的處理被實現(xiàn)。在20世紀初，滴慮是一種被證實了的處理系統(tǒng)。1914年，一個試驗方案確立了一個不同系統(tǒng)，空氣泡通過自由漂浮的好