環(huán)境科學(xué)和工程專業(yè)課程教案

1、第四單元閱讀材料：Reading Material : Analytical Technique and Methodology第八單元：空氣污染物的來源和類型第八單元 Reading Material : Type and Sources of Air Pollutants II J 閱讀材料：空氣污染物的類型和來源（）What are PCBs? 什么是多氯聯(lián)苯？There are 209 possible chlorinated biphenyls, ranging in physical characteristics. 大概有209種氯化聯(lián)苯，其物理性質(zhì)不同。The mono-and

2、 dichloro biphenyls ( 27323-18-8), ( 25512-42-9) are colorless crystalline compounds that when burned in air give rise to soot and hydrogen chloride. 一氯聯(lián)苯和二氯聯(lián)苯（27323-18-8），（25512-42-9）是無色晶體的化合物，當(dāng)它們?cè)诳諝庵腥紵龝?huì)產(chǎn)生煙塵和氯化氫。The most important products are trichlorobiphenyls,tetrachlorobiphenyls, pentachlorobip

3、henyls and/ or hexachlorobiphenyls. 最重要的產(chǎn)品是三氯化聯(lián)苯，四氯聯(lián)苯，五氯聯(lián)苯和/或六氯聯(lián)苯。Chlorinated biphenyls are soluble in many organic solvents and in water only in the ppm range. 多氯聯(lián)苯可溶于有機(jī)溶劑和僅在水的百萬分之一ppm（part per million）的范圍內(nèi)溶解。Although chemically stable (including to oxygen of the air) they can be hydrolyzed tooxybi

4、phenyls under extreme conditions forming toxic polychlorodibenzofurans. 氯化聯(lián)苯易溶于在許多有機(jī)溶劑和水只有在的范圍內(nèi)的可溶性。雖然化學(xué)穩(wěn)定性（包括空氣中的氧氣）但是在一定條件下，多氯聯(lián)苯可水解氧化成二氧化苯極端條件下形成的有毒的多氯代苯并二噁英。The PCB class of compounds received substantial attention and notoriety when in 1968, in Japan,accidental poisoning occurred by cooking rice

5、 in bran oil contaminated by PCBs. 在1968年，多氯聯(lián)苯類化合物受到實(shí)質(zhì)性的的關(guān)注和得到臭名，日本用受到多氯聯(lián)苯污染的米糠油做飯的意外中毒事件。Over 1000 patients suffered from various morbid symptoms. 超過1000例患者出現(xiàn)各種病態(tài)癥狀。A similar poisoning occurred in Taiwan in 1979. Causative agents were considered to be coconaminants of PCBs such as polychlorinated d

6、ibenzofurans that are secondarily formed during heating of PCBs congeners in commercial PCB mixtures and require a second look at PCB toxicity. 1979年臺(tái)灣有一個(gè)類似的中毒事件。病原體被認(rèn)為是如多氯二苯并呋喃的多氯聯(lián)苯，其次是PCBs多氯聯(lián)苯同系物在商業(yè)PCB混合物在加熱過程中形成的，需要第二次看看PCB的毒性。PCB regulation多氯聯(lián)苯的管理Because of concerns regarding PCB s health effect

7、s and evidence of presence and persistence in the environment further manufacture of the chemical was banned under The 1976 Toxic Substance Control Act. 由于擔(dān)心多氯聯(lián)苯對(duì)健康的影響和證明存在以及持續(xù)在環(huán)境中會(huì)進(jìn)一步制造化學(xué)物質(zhì)的，在1976年美國有毒物質(zhì)控制法中被禁止了。PCB regulations provide deadlines for removal of most in-use capacitors and transformer

8、s containing PCBs and limit time for storage for disposal to one year. 多氯聯(lián)苯的管理提出最后期限為了最大去除使用電容器和變壓器逗留的多氯聯(lián)苯和限制儲(chǔ)存一年就要處理。EPA has allowed continued use of PCBs in electrical transformers and capacitors when the agency did not pose unreasonable risk. 當(dāng)經(jīng)銷產(chǎn)品不會(huì)產(chǎn)生過度的危險(xiǎn)時(shí)，環(huán)境保護(hù)局允許繼續(xù)使用含多氯聯(lián)苯的電子電容器和變壓器。Capacitors,

9、 except those in isolated areas should have been removed by October 1988, and transformers of a certain size in or near commercial buildings should be removed by October 1990. 電容器，除了那些分散地方的應(yīng)該被移走在1988年10月之后，變壓器的某一些型號(hào)和靠近商業(yè)建筑的應(yīng)該被移走在1990年10月后。EPA regulations require that PCBs taken out of service be dis

10、posed of either by specially designed high temperature incinerators needed to break high concentrations of PCBs to harmless components or by alternate destruction methods approved by the agency. Environmental Protection Agency 美國環(huán)保署，法規(guī)要求PCB服務(wù)多氯聯(lián)苯或者處置的，通過特別設(shè)計(jì)的高溫焚化爐需要打破高濃度的多氯聯(lián)苯的無害組件或替代由該機(jī)構(gòu)批準(zhǔn)的銷毀方法。Oils

11、 contaminated with low concentrations (50-500ppm) may be disposed by high efficiency boilers. 低濃度（50500PPM）污染的油可以通過高效率的鍋爐處理。The limited number of incinerators approved for PCB incineration and the high cost of building additional incinerators have given incentive for alternate destruction methods. A

12、lternate technologies must be capable of operating as effectively as EPA s incineration efficiency. 批準(zhǔn)用于焚燒多氯聯(lián)苯的焚燒爐數(shù)量被限制和成本高且附有焚燒爐的建筑鼓勵(lì)使用一一分解的方法。選擇的技術(shù)的運(yùn)轉(zhuǎn)效率必須能夠達(dá)到環(huán)境保護(hù)局的焚燒效率。PCBs in electrical transformers 多氯聯(lián)苯的電流體變壓器There were 304 million lb of PCBs used as electrical fluid in approximately 150000 ask

13、arel ( non-flammable electrical fluid) transformers in the United States. 在美國有304百萬磅的多氯聯(lián)苯被當(dāng)做電流體使用，大約150000阿斯卡列（不易燃的電流體）變壓器。About 70000 PCB transformers are in or near commercial buildings that are open to the public. 大約70000多氯聯(lián)苯變壓器建在或靠近對(duì)公眾開放的商業(yè)建筑。About 40000 of these transformers are owned by electr

14、ical utilities. Approximately 15000 of these transformers are used in the food and feed industry. 大約40000這些變壓器缺少電設(shè)施。大約15000這些變壓器被使用在食品和飼料工業(yè)。Utilities and other industries must maintain or dispose of approximately 150000 askareltype transformers that may develop leaks. 公用事業(yè)等行業(yè)必須保持或處置約150000氯代聯(lián)苯型變壓器可能

15、出現(xiàn)的漏洞。 Each year, an estimated 317 askarel-type transformers can be expected to leak. Each will lose about 5. 3 gal or 66 lb of PCBs. 公共設(shè)施和其他工業(yè)必須維護(hù)或處理大約150000阿斯卡列型變壓器可能產(chǎn)生的泄露，每一年，估計(jì)317阿斯卡列型變壓器被暴露泄露，將損失5.3/s或66磅多氯聯(lián)苯。Transformers classification變壓器的分類The EPA has three classification for transformers: 環(huán)保

16、局已對(duì)變壓器三分類： PCB transformers contain 500 or more ppm PCBs. 多氯聯(lián)苯變壓器，多氯聯(lián)苯含量在百萬分之500或超過百萬分之一。They must be inspected quarterly for leaks, and detailed records must be kept. 每季度被檢查出的泄露會(huì)被詳細(xì)的記錄并保存。No maintenance work involving removal of the core is allowed .除去核心沒有維持工作涉及的是被允許的。At the end of the transformers

17、 useful life, it must be destroyed in an EPA-approved facility, or the transformer liquid must be incinerated and the carcass landfilled. 在變壓器有效壽命的盡頭，它會(huì)被環(huán)境保護(hù)局支持的設(shè)施銷毀，或變壓器的液體被焚燒和外殼被掩埋。The courts and the EPA have held the original transformer owner liable for leakage that may occur for as long as the

18、carcass remains in the landfill. 環(huán)境保護(hù)局要呼吁變最初壓器擁有者對(duì)液體泄漏負(fù)責(zé)任并且提供足夠大的場(chǎng)地對(duì)變壓器掩埋。PCB-contaminated transformers contain between 50 and 400 ppm PCBs and require annual inspection. The rule concerning disposal, maintenance, and record keeping are less restrictive and less costly than those for PCB transformer

19、s. 受多氯聯(lián)苯污染的變壓器，多氯聯(lián)苯含量在百萬分之50至百萬分之400之間和要求必須每年檢查。管理涉及處理、維護(hù)、記錄保持在最小限制或者接近多氯聯(lián)苯變壓器要求的含量。Non-PCB transformers have less than 50 ppm PCBs and are exempt from the burdensome rules and requirements that apply to PCB and PCBs contaminated transformers. 沒有多氯聯(lián)苯的變壓器，多氯聯(lián)苯含量少于百萬分之50和免除了一些繁雜的規(guī)則和要求比在應(yīng)用于多氯聯(lián)苯變壓器和受多氯聯(lián)

20、苯污染的變壓器。NonPCB transformers are granted favor under the Toxic Substances Control Act. 沒有多氯聯(lián)苯的變壓器被包含在美國有毒物質(zhì)控制法里。 Analysis of PCBs 多氯聯(lián)苯分析Analytical methods most frequently used for detecting chlorinated biphenyls are capillary column gas chromatography coupled with mass spectrometry in the MID ( Multi

21、ple Ion Detection) mode and capillary column gas chromatography with ECD ( Electron Capture Detector). 分析法最頻繁用于發(fā)現(xiàn)含氯聯(lián)苯，在多離子檢測(cè)的模式下頂空毛管氣象色譜與質(zhì)譜分析結(jié)合、頂空毛管氣象色譜與電子捕獲測(cè)器結(jié)合。HPLC ( High Pressure Liquid Chromatography) and infrared spectroscopy are applicable to a limited extent. 高效液相色譜和紅外光譜適用于限制的范圍。Summary PCB

22、determinations are also possible, though not usual. These require exhaustive chlorination and measurement of the decachlorbipheny content or dechlorination and subsequent biphenyl measurement.總結(jié)，多氯聯(lián)苯的測(cè)定盡管不常用，也是有可能的。這是需要徹底的氯化作用好十氯聯(lián)苯內(nèi)容的測(cè)定或者脫氯后聯(lián)苯的測(cè)定。Infrared tested on PCBs多氯聯(lián)苯的紅外測(cè)試Infrared thermal trea

23、tment technology was field tested for effectiveness on PCBs contaminated soil at two Superfund sites during 1986. 在1986年期間，紅外熱治療技術(shù)在倆個(gè)超級(jí)基金地被現(xiàn)場(chǎng)檢測(cè)受多氯聯(lián)苯污染的土地的有效性。The transportable pilot system consisted of a primary furnace through which solid/ semisolid wastes were conveyed on a wire mesh belt. 移動(dòng)式試驗(yàn)系是

24、由一個(gè)一次火爐通過固體/半固體廢物被傳送到鋼絲網(wǎng)運(yùn)輸帶。The heat source was supplied by electric glow bars in lieu of gaseous fuels. 火源通過發(fā)電光棒代替氣體燃料提供。 Residence times and furnace temperatures could be controlled manually or automatically giving uniform ash. 為了提供均化灰分，停留時(shí)間和燃燒爐溫度可以手動(dòng)或自動(dòng)控制。A secondary chamber, heated by electric o

25、r gaseous fuels, followed the primary furnace and provided temperatures m excess of 220 F. The system was designed to comply with all RCRA and TSCA requirements.二次火爐通過電或氣體燃料加熱，與一次火爐一樣和提供的溫度超過2200F。系統(tǒng)被設(shè)計(jì)成符合資源保護(hù)和回收法案以及美國有毒物質(zhì)控制法要求。Select from Paul N. C. , High hazardous pollutants, Asestos, PCBs, dioxi

26、ns, biomedical wastes, PollutionEngineering, Vol. 21, No. 2, 1989unit 12 Text: Water Pollution and Pollutants第十二單元：水污染與污染物The relationship between polluted water and disease was firmly established with the cholera epidemic of 1854 in Londo, England. Protection of public health, the original purpose

27、of pollution control, continues to be the primary objective in many areas. 1854年英國倫敦爆發(fā)了大規(guī)模的流行性霍亂。此事明確地證實(shí)了污水和疾病之間的關(guān)系。當(dāng)初以公共健康為目的所采取的污染控制，依然是許多地區(qū)的主要目的。 However, preservation of water resources, protection of fishing areas, and maintenance of recreational waters are additional concerns today. 然而，水資源的保持，

28、產(chǎn)魚區(qū)的防護(hù)，以及娛樂活動(dòng)用水的維持在今天也成為關(guān)注的焦點(diǎn)。Water pollution problems intensified following World War II when dramatic increases in urban density and industrialization occurred. 緊隨第二次世界大戰(zhàn)之后所產(chǎn)生的城市人口密度突增和工業(yè)化進(jìn)程的加劇，都使得水污染問題越見明顯。Concern over water pollution reached a peak in the mid-seventies.致使對(duì)于水污染的關(guān)注程度在70年代中期達(dá)到了頂峰。

29、Water pollution is an imprecise term that reveals nothing about either the type of polluting material or its source. The way we deal with the waste problem depends upon whether the contaminants are oxygen demanding, algae promoting, infectious, toxic, or simply unsightly. 水污染是一個(gè)不準(zhǔn)確的術(shù)語，它并未指出污染物的種類和來源

30、。而我們處理廢水問題的方式往往取決于以下幾個(gè)方面：污染物是否需要氧氣，是否助長藻類，是否有傳染性，是否有毒，或者僅僅是否好看。 Pollution of our water resources can occur directly from sewer outfalls or industrial discharges (point sources) or indirectly from air pollution or agricultural or urban runoff ( nonpoint sources). 水源的污染可能直接來自生活污水的排放或工廠污水排放（點(diǎn)源），也可能間接地由

31、空氣污染、農(nóng)業(yè)排水或城市排水（非點(diǎn)源）所引發(fā)。 Chemically pure water 1s a collection of H2 0 molecules-nothing else. 化學(xué)上所謂的純水僅僅是水分子的集合。Such a substance is not found in nature-not in wild streams or lakes, not in clouds or rain, not in falling snow, nor in the polar ice caps. 無論在野外的河流或湖泊、云層或雨水中，還是在下雪期間，極地的冰帽地區(qū)，這種物質(zhì)在自然界均不能找

32、到。Very pure water can be prepared in the laboratory but only with considerable difficulty. 然而在實(shí)驗(yàn)室中可以制備非常純凈的水，但是存在一定的困難。Water accepts and holds foreign matter.因?yàn)樗畼O易接受和容納外來物質(zhì)。 Municipal wastewater, also called sewage, is a complex mixture contammg water( usually over 99 percent) together with organic

33、and inorganic contaminants, both suspended and dissolved. 城市污水，也被稱作生活污水，是一種復(fù)雜的混合物，它包含水（通常超過99）以及懸浮或溶解的有機(jī)和無機(jī)污染物。The concentration of these contaminants is normally very low and is expressed in mg/L, that is, milligrams of contaminant per liter of the mixture. 這些污染物的濃度通常很低并且以mg/L來表示，也就說，每升混合物含有多少毫克污染物

34、。This is a weight-to-volume ratio used to indicate concentrations of constituents in water, wastewater, industrial wastes, and other dilute solutions.重量與體積比也常用來表示在水、廢水、工業(yè)廢水和其它稀釋溶液中的污染物濃度。 Microorganisms. Wherever there is suitable food, sufficient moisture, and an appropriate temperature, microorgan

35、isms will thrive. 微生物 任何地方只要存在適合的食物，充足的濕度和適當(dāng)?shù)臏囟?，微生物即可大量繁殖?Sewage provides an ideal environment for a vast array of microbes, primarily bacteria, plus some viruses and protozoa. 而生活污水為各種各樣的微生物提供了一個(gè)理想的環(huán)境。這些微生物主要是細(xì)菌，某些病毒和原生動(dòng)物。Most of these microorganisms in wastewater are harmless and can be employed

36、in biological processes to convert organic matter to stable end products. 廢水中的大多數(shù)微生物是無害的，并且可借助生化過程，將有機(jī)物轉(zhuǎn)化為穩(wěn)定的最終產(chǎn)物。However, sewage may also contain pathogens from the excreta of people with infectious diseases that can be transmitted by contaminated water. 但是當(dāng)一些人患有可通過有毒廢水傳播的傳染性疾病時(shí)，其排泄物所攜帶的致病病原體，極有可能成

37、為污水的組成部分。 Waterborne bacterial diseases such as cholera, typhoid, and tuberculosis, viral diseases such as infectious hepatitis, and the protozoan-caused dysentery, while seldom a problem now in developed countries, are still a threat where properly treated water is not available for public use. 雖然在

38、發(fā)達(dá)國家，類似于水傳播的細(xì)菌性疾病，例如霍亂、傷寒和肺結(jié)核，病毒性疾病例如傳染性的肝炎和原生蟲引起的痢疾，已經(jīng)不再是問題，但是在那些經(jīng)過適當(dāng)處理過的污水不能被公共利用的地區(qū)仍然存在著很大威脅。Tests for the few pathogens that might be present are difficult and time consuming, and standard practice is to test for other more plentiful organisms that are always present ( in the billions) in the in

39、testines of warm-blooded animals, including humans.對(duì)于少量存在的病原體的檢測(cè)是相當(dāng)困難和耗時(shí)的。其標(biāo)準(zhǔn)做法是檢測(cè)存在于包括人類在內(nèi)的（數(shù)十億）熱血?jiǎng)游锬c胃中的有機(jī)物。 Solids. 固體The total solids ( organic plus inorganic) in wastewater are, by definition, the residues after the liquid portion has been evaporated and the remainder dried to a constant weight

40、at 103. 廢水中的總固體（包括有機(jī)的和無機(jī)的）是指液體部分被蒸發(fā)，并且在103烘干至恒重的殘余物。 Differentiation between dissolved solids and undissolved, that is, suspended, solids are accomplished by evaporating filtered and unfiltered wastewater samples. 區(qū)分可溶性固體和懸浮固體的方法，是通過蒸發(fā)過濾的和沒有通過過濾的廢水樣品來進(jìn)行的。The difference in weight between the two drie

41、d samples indicates the suspended solids content. 兩種烘干樣品質(zhì)量的差值即表示懸浮物的質(zhì)量。To furt her categorize the residues, they are held at 550C for 15 minutes. The ash remaining is considered to represent inorganic solids and the loss of volatile matter to be a measure of the organic content.將殘留物在550溫度下保持15分鐘以進(jìn)一步

42、分類，剩余的灰代表了無機(jī)物，失去的揮發(fā)物則代表有機(jī)物的重量。 Suspended solids (SS ) and volatile suspended solids ( VSS ) are the most useful. 懸浮固體（SS）和揮發(fā)性的懸浮固體（VSS）是最有用的。SS and BOD (biochemical oxygen demand) are used as measures of wastewater strength and process performance. SS和BOD（生化需氧量）是廢水的受污染程度及其過程性能的指標(biāo)。VSS can be an indic

43、ator of the organic content of raw wastes and can also provide a mea:mre of the active microbial population in biological processes. VSS可以指示廢水中有機(jī)物的含量，也可以衡量在生化過程里活性的微生物群。 Inorganic constituents. The common inorganic constituents of wastewater include: 無機(jī)成分 廢水中常見的無機(jī)成分包括： 1.Chlorides and sulphates. Nor

44、mally present in water and in wastes from humans. 1氯化物和硫酸鹽。常見于人類排放的廢水和廢物中。 2.Nitrogen and phosphorousD . In their various forms ( organic and inorganic ) in wastes from humans, with additional phosphorous from detergents. 2氮和磷。以各種形式（有機(jī)的和無機(jī)的）存在于來自人類排放的廢物，和含磷的清潔劑。 3. Carbonates and bicarbonates . Norm

45、ally present in water and wastes as calcium and magnesium salts. 3碳酸鹽和碳酸氫鹽。通常以鈣鹽和鎂鹽的形式出現(xiàn)在水和廢物中。 4. Toxic substances. Arsenic, cyanide, and heavy metals such as Cd, Cr, Cu, Hg, Pb, and Zn are toxic inorganics which may be found in industrial wastes.4有毒物質(zhì)。砷，氰化物和在工業(yè)廢水中可以找到的有毒無機(jī)物：Cd（鎘）、Cr（鉻）、Hg（汞）、Pb（鉛）

46、、Zn（鋅）等重金屬。 In addition to these chemical constituents, the concentration of dissolved gases, especially oxygen, and the hydrogen ion concentration expressed as pH are other parameters of interest in wastewater. 除了這些化學(xué)成分，溶解氣體的濃度，尤其是氧氣，用pH值所表示的H離子的濃度也是其它引起廢水注意的指標(biāo)。 Organic matter. 有機(jī)物 Proteins and car

47、bohydrates constitute 90 percent of the organic matter in domestic sewage. 生活污水中的有機(jī)物90是由蛋白質(zhì)和碳水化合物組成。The sources of these biodegradable contaminants include excreta and urine from humans; food wastes form sinks; soil and dirt from bathing; washing, and laundering; plus various soaps, detergents, and

48、other cleaning products.這些可生物降解的物質(zhì)包括人類的尿和排泄物、洗滌槽的食物殘?jiān)?、土和洗澡的臟物、洗衣用水和洗燙水，及各種肥皂、洗潔精和其他清潔產(chǎn)品。 Various parameters are used as a measure of the organic strength of wastewater. 各種指標(biāo)用來衡量廢水中有機(jī)物濃度。One method is based on the amount of organic carbon ( total organic carbon, or TOC ) present in the waste. 一種方法是基于

49、廢水中的有機(jī)碳的總量（即總有機(jī)碳TOC）。TOC is determined by measuring the amount of C02 produced when the organic carbon in the sample is oxidized by a strong oxidizer and comparing it with the amount in a standard of known TOC. 總有機(jī)碳是由樣品中有機(jī)碳被強(qiáng)氧化劑氧化成二氧化碳的數(shù)量與已知的總有機(jī)碳的標(biāo)準(zhǔn)數(shù)量的比較所決定的。 Most of the other common methods are bas

50、ed on the amount of oxygen required to convert the oxidizable material to stable end products. 常見的另一種方法是根據(jù)把氧化物轉(zhuǎn)化成穩(wěn)定的最終產(chǎn)物所需要的氧氣。Since the oxygen used is proportional to the oxidizable material present, it serves as a relative measure of wastewater strength. The two methods used most frequently to det

51、ermine the oxygen requirements of wastewater are the COD and BOD tests. 因?yàn)樾柩趿空扔谖鬯鞋F(xiàn)存的氧化物，它可以用于廢水濃度的相對(duì)衡量。通常確定廢水需氧量的兩種方法是COD（化學(xué)需氧量）和BOD（生化需氧量）的測(cè)定。The COD, or chemical oxygen demand, of the wastewater is the measured amount of oxygen needed to chemically oxidize the organics present; the BOD, or bioch

52、emical oxygen demand, is the measured amount of oxygen required by acclimated microorganisms to biologically degrade the organic matter in the wastewater. 化學(xué)需氧量，是用化學(xué)方法氧化有機(jī)物的需氧量。而生化需氧量，是通過適應(yīng)環(huán)境的微生物的以生物的方式降解廢水中的有機(jī)物的需氧量。 BOD is the most important parameter in water pollution control. It is used as a mea

53、sure of organic pollution, as a basis for estimating the oxygen needed for biological processes, and as an indicator of process performance. 在水污染控制理論中，生化需氧量是最重要的參數(shù)。生化需氧量用于測(cè)定有機(jī)物污染，是評(píng)估生物反應(yīng)需氧量的基礎(chǔ)和反應(yīng)過程的指標(biāo)。 The amount of organic matter in water or wastewater can be measured directly ( as TOC, for example

54、), but this doesn t tell us whether the organics are biodegradable or not. 我們可以直接地測(cè)定水或者廢水中的有機(jī)物含量（例如測(cè)定總有機(jī)碳），但是這并不能告訴我們有機(jī)物是否有被生物降解。 To measure the amount of biodegradable organicsCD , we use an indirect method in which we measure the amount of oxygen used by a growing microbial population to convert (

55、 oxidize) organic matter to C02 and H2 0 in a closed system. 為了測(cè)定可生物降解的有機(jī)物量，我們用一種間接的方法，也就是在一個(gè)封閉的系統(tǒng)里，測(cè)定將有機(jī)物轉(zhuǎn)化（氧化）成二氧化碳和水所用的生長的微生物群的耗氧量。The oxygen consumed, or biochemical oxygen demand (BOD), is proportional to the organic matter converted, 耗用的氧氣，或生化需氧量，正比于有機(jī)物的轉(zhuǎn)化量，and therefore BOD is a relative meas

56、ure of the biologically degradable organic matter present in the system. 因此，生化需氧量是系統(tǒng)中生物降解有機(jī)物的相對(duì)衡量。Because biological oxidation continues indefinitely, the test for ultimate BOD has been arbitrarily limited to 20 days, when perhaps 95 percent or more of the oxygen requirement has been met.因?yàn)樯镅趸^程可以無

57、限次地進(jìn)行，最終生化需氧量的測(cè)定被限定為20天，這個(gè)時(shí)間能夠滿足95%或以上的微生物氧氣需求。Even this period, however, is too long to make measurement of BOD useful, 但是過程時(shí)間過長，致使生化需氧量的測(cè)定沒有效用， so a five-day test, BODs , carried out at 20C, has become standard.所以一種五天式的測(cè)定，即將水樣置于20的黑暗環(huán)境五天，作為生化需氧量的標(biāo)準(zhǔn)。The rate of the BOD reaction depends on the type

58、of waste present and the temperature and is assumed to vary directly with the amount of organic matter (organic carbon) present.生化需氧量的反應(yīng)速度取決于存在的廢水類型、溫度以及假設(shè)其隨著存在的有機(jī)物（有機(jī)碳）的數(shù)量的變化趨勢(shì)。Unit 14Text: Water PurificationWater molecules have no memory, and therefore his silly to talk about the number of times t

59、hat the water you drink has been polluted and repurified, as if the molecules gradually wore out. 水分子是沒有記憶力的，所以談?wù)摫晃廴竞捅粌艋娘嬘盟拇螖?shù)是沒意義的，例如分子的逐漸損耗。All that is important is how pure it is when you drink it.而當(dāng)我們飲水的時(shí)候到底它有多純凈才是最重要的。 The purification of water has developed into an elaborate and sophisticated

60、 technology. 水的凈化已經(jīng)發(fā)展為一項(xiàng)復(fù)雜的和尖端的技術(shù)。However, the general approaches to purification should be comprehensible, and in some cases even obvious, from a general understanding of the nature of water pollution. 然而，污水凈化的本質(zhì)的總方法是容易理解的，在某些情況下也是明顯的。 Impurities in water were classified as suspended, colloidal, or