(完整版)給排水畢業(yè)論文設(shè)計(jì).doc

1、優(yōu)秀論文審核通過未經(jīng)允許切勿外傳DisinfectionDisinfection involves destruction or inactivation of organisms which may be objectionable from the standpoint of either to those responsible for supplying water, design of facilities for disinfection must necessarily be carefully executed.a. Chlorination. The application

2、of chlorine to water is the preferred method of disinfecting water supplies at military installations.(1) Definitions. Terms frequently used in connection with chlorination practice are defined as follows:(a) Chlorine demand. The difference between the concentration of chlorine added to the water an

3、d the concentration of chlorine remaining at the end of a specified contact period. Chlorine demand varies with the concentration of chlorine applied, time of contact, temperature, and water quality.(b) Chlorine residual.The total concentration of chlorine remaining in the water at the end of a spec

4、ified contact period,(c) Combined available residual chlorine. Any chlorine in water which . The most common source of nitrogen is ammonia, and compounds formed by the reactions between chlorine and ammonia are known as chloramines. The disinfecting power of combined available chlorine isabout 25 to

5、 100 times less than that of free available chlorine. (d) Free available residual chlorineThat. part of the chlorine residual which .(2) Chlorination practice.(a) Combined residual chlorination, Combined residual chlorination entails the application of sufficient quantities of chlorine and ammonia,

6、if ammonia is not present in the raw water, to produce the desired amount of combined available chlorine (chloramine) in a water. If enough ammonia is present in raw water to form a combined chlorine residual, only chlorine need be added to the water. Combined residual chlorination is generally used

7、 only when maintaining an adequate free chlorine residual in the distribution system is difficult or when objectionably . Due consideration of other TTHM control alternatives should be made before using chloramines,(see para 2-13).(b) Breakpoint chlorination.If a water contains - ammonia or certain

8、nitrogenous organic matter which reacts with chlorine, the addition of chlorine causesthe formation of chloramines until the ratio of elemental chlorine to ammonia compounds is about 5 to 1. Further addition ofchlorine results in the oxidation of chloramines to gaseousnitrogen and nitrogen oxides, w

9、hich decreases the quantity of chloramines present. After all of the chloramines oxidized, additional chlorine added to the water forms only free available chlorine. The point at which all of the chloramines oxidized and only free chlorine is formed is called the“ breakpoint . If“no ammonia is prese

10、nt in the water, there will be no breakpoint.The chlorine required to reach the breakpoint is usually about 10times the ammonia nitrogen contentof the water. However, in certain waters, because of the presence of other chlorine consuming substances, as much as 25 times the ammonia nitrogen concentra

11、tion may be required. Enough chlorine should be added past the breakpoint to ensure an adequate free chlorine residual.(c) Marginal chlorination. Marginal chlorination involves the application of chlorine to produce a desired level of total chlorine residual regardless of the relative concentrations

12、 of free or combined chlorine present. In marginal chlorination the initial chlorine demand satisfied but some oxidizable substances remain.(d) Chlorine dosages.Figure 2-4 provides minimum cysticidal and bactericidal free chlorine residuals and minimum bactericidal combined chlorine residuals for va

13、rious pH and temperature levels. Since waterbornebacteria are the major concern at fixed installations, minimum bactericidal levels will be maintained in treated water in all parts of the distribution system under constant circulation. Even at lower pH levels, free chlorineresiduals should not fall

14、below 0.2 mgL and combined chlorine residuals should not fall below 2.0 mgL. If marginal chlorination is practiced, thetotal chlorine residual must not beless than2.0mgl. Wheneverepidemological evidence indicates anoutbreakofa nonbacterialwaterborne disease such as amebiasis, infectiousthe area of a

15、 fixedmilitary installation, cysticidal free chlorine residuals shall be maintained in the water supply. Further guidance on disinfection requirements may beobtained from the Surgeon General s officeAirForce. policy on minimum chlorine levels is established in AFR 161-44.(3) Other effects of chlorin

16、ation. In addition to the disinfectionachieved with chlorination, other beneficial effects should be noted. Sincethe oxidizing power of chlorine is the presence of free chlorine, sulfide is oxidized, nitrites are oxidized to nitrates, and soluble iron andmanganese are oxidized to their insoluble oxi

17、des. Free chlorine also reacts with naturally occurring taste, odor and colorproducing organic substancesto form chloro-organic compounds,e.g., trihalomethanes (see para 2- 13.b.).The US EPA, after much discussion over costs benefits, a maximum contaminant level for serving above 10,000 persons and

18、disinfection practices will be required.(4) Application of chlorine. Chlorine may be applied to water of twoforms: As gaseous elemental chlorine or as at all fixed installations. Thecost of all plants larger than 0.5 mgd. For remote sites at fixed installations, some well sources require 5 gpm or le

19、ss. These sources with small demands can use .(a) Point of application.Chlorine may be applied to water in a variety of locations in the water treatment plant, storage facilities, or distribution system. It is absolutely essential that the chlorine applied to the water be quickly and thoroughly mixe

20、d with the water undergoing treatment. If required, special chlorine mixing facilities should be provided. In conventional water treatment plants, chlorine may be applied. prior to any other treatment process (prechlorination), following one or more of the unit treatment process (postchlorination),

21、and again in the more distant points of the distribution system (dechlorination).1 Prechlorination., Prechlorination been used so the water would maintain a chlorine residual for the entire treatment period, thus lengthening the contact time. The coagulation, flocculation,and filtration processeswer

22、e thought to be improved by prechlorination of the water, and nuisance algae growths in settling basins were reduced. Inprechlorination, the chlorine was usually injected into the raw water at or near the raw water intake. Prechlorination was the most accepted practice of disinfection in the past. H

23、owever, since many surface waters containTHM precursors that will combine with the free chlorine during prechlorination and form potentially carcinogenic THMs, such aschloroform, the point of application shifted further down the treatment process to take advantage of precursor removal during treatme

24、nt.2 Postchlorination. Postchlorination generally involves the application of chlorine immediately after filtration and ahead of the clear well. The design and construction of water treatment plants for military installations will include the necessary provisions for changing the locations of chlori

25、ne applications as may later be desirable for improving treatment or disinfection processes.3 Dechlorination. Dechlorination is the practice of adding chlorine to water in the distribution system to maintain a minimum chlorine residual throughout the system.(b) Chlorination equipment.Hypochlorite sa

26、lts must be applied to the water in solution form. Hypochlorite solutions are pumped by a diaphragm pump through an injection system into the water to be chlorinated. If elemental chlorine is used for disinfection, it shall be injected bysolution-type chlorinators. Since chlorine solutions are acidi

27、c, many components of a chlorination system must be constructed of corrosion resistant materials such as glass, silver, rubber, or plastics. Maintaining the chlorination apparatus in a trouble-free state is essential, Key spare parts and repair kits for chlorination systems must be kept on system sh

28、all be installed in duplicate.(c) Automatic control.If automatic chlorination control is utilized, the chlorine feed rate should be controlled primarily by the rate of flow of water, with a signal from a downstream residual chlorine analyzer used to trim the feed rate. Provision for manual control d

29、uring emergency situations must be included.(5) Superchlorination and dechlorination. Superchlorination may be necessaryif there are large variations in chlorine demand or if availablecontact time is brief. Water which superchlorinated generally requires dechlorination before discharge to the distri

30、bution system. Dechlorination may be achieved through the application of sulfur dioxide, sodium bisulfite, or sodium sulfite, or by passing the water through granular activated carbon filters. The dechlorination process (and subsequent dechlorination, if necessary) shall be controlled so that the fr

31、ee residual chlorine remaining in the water is at least 0.2 mgL. Careful monitoring must be practiced to assure that potentially table 2-5(6) Safety precautionsfor chlorination. The AWWAmanual “ SafetyPractice for Water Utilitiescontains” safety recommendationsregardingthe use of chlorine. These rec

32、ommendations shall be followed at all military water treatment facilities. Further discussion on safe operation ofchlorination facilities for Army installations are contained in TB MED 576, appendix L.b. Alternate DisinfectantsIf. the use of chlorine as a disinfectant causes unacceptably large conce

33、ntrations of chlorinated organic compounds, andif all other methods for reducing TTHM exhausted,such as moving the point of chlorination, aeration, and special coagulant (as shown in table 2-3 for chloroform which is the main constituent of TTHMs in many cases)and if an alternate raw water source, s

34、uch as a ground water source, is not available, an alternative disinfectant must be considered. Any alternate disinfectant system installed as the primary means of water disinfection shall facilities available and operative for stand-by use. Five alternative disinfectants are discussedbelow; ozone,

35、chlorine dioxide, chloramines,ultraviolet (UV) radiation, and UV and Ozone combined. While chlorine is the least costly disinfectant, considering dosageand energy consumption basis. However alternate disinfectants are not significantly more expensive.(1) Ozone. Ozone is an extremely powerful disinfe

36、ctant thatused inEurope either as a sole disinfectant, orin conjunctionwithpostchlorination to impart a persistent chlorineresidual in thewaterdistribution system. United States potable waterplants the past usedozone to control taste and odor. Today ozonation is being increasingly used as a primary

37、disinfectant prior to rapid mixing, floccula- . tion and filtration. Ozonation does not produce THMs. It is reduced to oxygen and does not leave any residual disinfectant. Hence, the need for postchlorination. Ozone is generated electrically, as needed using the electric discharge gap (corona) techn

38、ique. Air or oxygen stream, a coolingwater stream and alternating electric current are required. Efficient cooling is essential to reduce thermal decomposition of ozone. Bubble diffusers appear to be the most economic ozone contractors available.(2) Chlorine Dioxide, Chlorine dioxide is a the presen

39、ce of their precursors. Chlorine dioxide uses in the United Stateslimited to taste and odor control although it used elsewhere as a primary disinfectant and ispresently receiving more attention in the United States. The common method of chlorine dioxide production is to react chlorine gas from a con

40、ventional chlorinator with a sodium chlorite solution. Following the mixing of the chlorine and sodium chlorite streams and prior to introduction into the main stream the mixed stream is passed through a packed column contactor to maximize chlorine dioxide production. A major disadvantageof chlorine

41、 dioxide is the formation of chlorate and chlorite which are potentially toxic.-. (3) Chloramines, The use of chloramines as a disinfectant fell into disuse after the introduction of breakpoint chlorination. To achieve the same disinfection ability of chlorine, 10 to 15 times the amount of chloramin

42、es are needed or longer contact time is required.More chloramines are needed if the influent water, Chloramines are easy to generate, feed, and produce a persistant residual that will remain through the water distribution system. Chloramines may be produced by introducing ammonia to the water stream

43、 prior to the addition of free chlorine. This process can be optimized for minimum THM production and maximum disinfection. Recently some concern over chloramine toxicity.(4) Ultraviolet Radiation. Ultraviolet (UV) radiationused on a largescale for drinking watersupply disinfection. Most ofits uses

44、includeproduct or processwater disinfection whereused to disinfect drinkingwater at remotely locatedcruise ships. Few large scale water processingplants use UV disinfection, although itsapplicationis feasible. UVdisinfection does not leave a disinfectant residualand should beaccompanied by postchlor

45、ination. Ultraviolet irradiation is also effective in oxidizing organic compounds in water, Water turbidity will inhibit the effectiveness of UV disinfection.(5) UV and Ozone, Recently there some experimentation in a combined UV and ozone contactor. Results from these tests show promise. However, th

46、ere is no known water treatment plant operating with this method of disinfection.消毒消毒包括去除和毀滅一些影響人體健康和感官的有機(jī)物。消費(fèi)者對(duì)健康水的供應(yīng)是首要關(guān)心的，消毒設(shè)施的設(shè)計(jì)必須小心謹(jǐn)慎。一、加氯消毒加氯消毒是軍事裝備供水首要的消毒方法（ 1）定義氯化的普遍應(yīng)用實(shí)踐介紹如下a.氯需求量加在水中氯的濃度與最后水中的氯的濃度是有一定的差異的，氯的需求量與氯氣的濃度，接觸時(shí)間，溫度，水質(zhì)有關(guān)。b.余氯經(jīng)過整個(gè)的接觸過程后留在水中的氯的濃度c.混合態(tài)使用余氯水中與氮?dú)饨Y(jié)合的氯氣。 水中常用的氮?dú)鈦碜园彼?將氯氣

47、與氨水混合可得到人們熟知的氯胺?；旌下鹊南灸芰Υ蠹s為游離態(tài)余氯的25%100% 。d.游離態(tài)可使用余氯沒有與氨氣結(jié)合的部分余氯。（ 2）氯化消毒的使用a. 氯化消毒剩余物的結(jié)合氯化消毒剩余物的結(jié)合必須應(yīng)用一些比較特別的氯和氨， 如果天然水中不含氨，在水中可提取到量的可使用的氯的結(jié)合物。b.氯化消毒斷點(diǎn)如果水中含有氨或某些可與氯反映的含氮有機(jī)物， 加入的氯將會(huì)引起反映直到氯與氮元素的化合比大約為 5： 1。進(jìn)一步添加氯氣，導(dǎo)致氮和氮氧化物減少， 降低了水中現(xiàn)存的氯化物的量。 所有的氯化物被氧化后，額外加入水中的氯將只會(huì)形成不可利用的氯。 所有氯化物被氧化形成不可用氯的這個(gè)點(diǎn)被稱為斷點(diǎn)。如果水中

48、不存在氨也就不存在斷點(diǎn)。氯化消毒達(dá)到斷點(diǎn)通常水中的氨氮比應(yīng)為10 倍，然而在海水中存在其他需要消耗氧的物質(zhì)時(shí)，有多達(dá)25 倍的氨氮必會(huì)被要求。為了確保足夠的游離余氯，斷點(diǎn)后應(yīng)加入充足的氯。c.邊際氯化邊際氯化不考慮游離態(tài)余氯和混合態(tài)余氯總余氯應(yīng)達(dá)到的水平，除了一些氧化物質(zhì)的存在，最初的邊際氯化應(yīng)得到滿足。d.氯使用量表 2-4 顯示了最少的游離態(tài)殺菌余氯與最小的混合態(tài)殺菌余氯在不同的溫度， PH 的情況下的效果。在固定裝置中，水煤細(xì)菌是首先應(yīng)考慮的因素。在指定的循環(huán)下， 最小殺菌水平將會(huì)體現(xiàn)各部分水的處理體系。即使在較低的 PH 值情況下，游離態(tài)余氯不應(yīng)低于 0.2 毫克升 ，混合態(tài)余氯不應(yīng)低

49、于 2.0 毫克升。邊際氯化實(shí)現(xiàn)了，總余氯不得少于 2.0 毫克升。在一個(gè)具有固定的軍事設(shè)施的地方也會(huì)有一些突發(fā)性的水疾病如傳染性肝炎，血吸蟲病。所以應(yīng)保持尤里余氯供水，進(jìn)一步的消毒措施也可在外科醫(yī)生的辦公室找到?？哲娊⒌淖畹陀嗦人降恼`判率為161-44.（ 3）其他影響氯化的因素為了實(shí)現(xiàn)氯化，其他有益的影響也應(yīng)注意。由于氯氧化能力強(qiáng)，再有游離態(tài)氯存在的情況下，硫化氫被氧化，亞硝酸鹽被氧化成硝酸鹽，可溶性鐵和錳被氧化成不可溶的。 游離態(tài)氯會(huì)伴隨著產(chǎn)生味道和香氣及含氯有機(jī)物如：三氯甲烷。美國(guó) EPA 通過對(duì)成本和效益的反復(fù)討論， 選擇了一條在 1000 人以上的，表明了水處理行業(yè)應(yīng)避免花費(fèi)在處理廠的裝飾上面。 為了達(dá)到美國(guó)在未來三氯甲烷最大的污染水平，更有意義的變化將會(huì)在氯化實(shí)踐中被要求。（4） 氯氣的應(yīng)用氯在水中有兩種存在形式，作為氣態(tài)氯元素或次氯酸鹽。 氣態(tài)氯元素可應(yīng)用在固定裝置中的水消毒。次氯酸鹽的使用大多在 0.5 百萬加侖日的工廠。一些固定裝置建的較遠(yuǎn)， 一些好的資源需要每分鐘 5 加侖或更少，這些需要量