水污染控制 課件

1、Chapter 3 Wastewater Treatment1 TermsSanitary sewage, municipal sewage, preliminary, primary, secondary/biological treatment, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), treatment/removal efficiency, primary effluent, sewage effluent/emission standard

2、s. Screen, grit chamber, primary/secondary clarifiers or settling tanks/basins, detention time, outlet weir. Microbe/microorganism, bacteria, fungi (fungus), activated sludge process, aeration tank/clarifier/basin, supernatant, ruturn/excess sludge, food-to-microorganism (F/M) ratio, mixed liquor su

3、spended solids (MLSS), sludge volume index (SVI), sludge bulking, process flow diagram.2 Flow chart of a wastewater treatment systemA flow chart showing the typical sequence of wastewater treatment processes is given in Figure 1, where screening, grit removal, and primary sedimentation are primary t

4、reatment processes. Secondary treatment usually involves biological processes and additional settling. Not all sewage treatment plants require tertiary (advanced) treatment of nitrogen and phosphorus. 廢水處理的典型工藝流程圖如圖1所示。篩濾、砂礫的去除、自然沉淀屬一級處理過程。二級處理通常包括生物處理和二次沉淀。Figure 1 Schematic overview of a wastewate

5、r treatment system不是所有廢水處理廠都需要去除氮和磷的三級或者深度處理。3 Primary treatmentIn a typical sequence of wastewater treatment processes, screening, grit removal, and primary sedimentation are primary treatment processes. Primary treatment processes include preliminary treatment and primary sedimentation. 3.1 Prelim

6、inary treatment systemsPreliminary treatment systems typically include screens and grit chambers.The first treatment process for raw wastewater is coarse screening. It retains floating debris such as wood, rags, or other bulky objects, that could clog pipes or damage mechanical equipment in the rest

7、 of the plant. 廢水的第一個處理過程是初格柵。它能去除懸浮碎片，比如木頭，碎屑或者其它大體積的物質，這些物質能堵塞處理廠后續(xù)處理設備的管道，或者損壞其機械設備。3.2 Primary sedimentationAlthough the grit will settle out at this reduced velocity, the lighter suspended organic solids will still be carried through to the next treatment unit. After preliminary treatment by sc

8、reening and grit removal, the wastewater still contains suspended organic solids that can be removed by plain sedimentation. 盡管沙礫在這個速度能沉降下來，密度較小的懸浮有機固體仍將進入下一個處理單元。通過格柵和砂礫預處理后，廢水中仍然含有能通過自然沉淀去除的懸浮有機固體。Settling tanks that receive sewage after grit removal are called primary clarifiers or tanks. They us

9、ually provide between 1 and 2 h of detention time. The tanks may be circular or rectangular in shape. Two or more clarifiers should be provided at all but the smallest treatment plants. 接受去除沙礫后廢水的沉淀池叫做初沉池。廢水在初沉池的停留時間通常為1 - 2 h。池子可以是圓形或者矩形。除規(guī)模最小的處理廠之外，初沉池應該有兩個或多個。Chemicals may sometimes be added to t

10、he primary clarifiers to promote the removal of very small or colloidal particles. Primary treatment usually can remove up to 60% of the suspended solids and about 35 % of the BOD from wastewater. In almost all cases, primary treatment must be followed by secondary treatment processes; tertiary trea

11、tment may also be required to protect sensitive bodies of water that receive the treated effluent (CdCx). 有時可以在初沉池中投加化學試劑以促進極小微粒或者膠體粒子的沉淀。一級處理通常能去除廢水中高達60%的懸浮固體，和約35%的BOD。幾乎所有的污水處理廠，一級處理后面必須有二級處理；為了保護敏感的受納水體，二級處理后必須接三級處理。4 Secondary or Biological TreatmentPrimary treatment processes remove only thos

12、e pollutants that will either float or settle out by gravity, but about half of the raw pollutant load still remains in the primary effluent (CdCx). The purpose of secondary treatment is to remove the suspended solids that did not settle out in the primary tanks and the dissolved BOD that is unaffec

13、ted by physical treatment (Cx). In the United States, secondary treatment processes are almost always biological systems. 初級處理僅僅去除懸浮的或者可以通過重力沉降的污染物，在一級處理的出水中，仍然殘留有約一半的未經處理的污染物。二級處理的目的是去除初沉池中沒有沉降的懸浮固體和不能通過物理處理去除的溶解的BOD。二級處理對BOD和TSS的平均去除率通常有85%。在美國，二級處理方法幾乎都是生物處理系統(tǒng)。Biological treatment of sewage invol

14、ves the use of microorganisms. The microbes, including bacteria and protozoa, consume the organic pollutants as food. As they metabolize the biodegradable organics, converting them into carbon dioxide, water, and energy for their growth and reproduction, they consume oxygen. The oxygen consumed is t

15、he dissolved oxygen (DO). 廢水的生物處理利用微生物，比如細菌，原生動物，它們以有機污染物為食。當微生物代謝可生物降解的有機物時，也就是轉化可生物可降解的有機物為二氧化碳、水和供自己生長和繁殖的能量時，它們消耗氧氣。消耗的氧氣稱為溶解氧。4.1 BODThe amount of DO used by microbes to decompose or stabilize the biodegradable organics in a given volume of water or wastewater is called BOD. The BOD is used as

16、an indirect measure of the total amount of biodegradable organics in the water. The more the organic material there is in the water, the higher the BOD exerted by the microbes will be. 在一定體積的水或者廢水中，微生物降解或者穩(wěn)定可降解有機物所消耗的溶解氧的數量叫做生化需氧量。BOD可以間接測量水中可生物降解的有機物的數量。水中有機物越多，微生物所氧化分解有機物所需的BOD就越高。The complete dec

17、omposition of organic material by microorganisms takes time, usually 20 d or more under ordinary circumstances/conditions/surroundings/environment. The amount of oxygen used to completely decompose all the biodegradable organics in a given volume of water is called the ultimate BOD. For example, if

18、a 1 L volume of municipal sewage requires 300 mg of oxygen for complete decomposition of the organics, the BOD would be expressed as 300 mg/L. 在一般的環(huán)境條件下，微生物完全降解有機物所需要的時間，通常為20天或以上。在一定體積的水中，微生物完全降解或者穩(wěn)定所有的可降解有機物所消耗的溶解氧的數量叫做最終的生化需氧量BODL。例如，如果完全降解1L城市污水中的有機物需要300 mg的氧，那么BODL為300 mg/L。The 20 d or so requ

19、ired for the ultimate BOD to develop is much too long a time to wait for lab results. This is particularly true when the BOD data are used to monitor the efficiency of a water pollution control plant. 測定最終生化需氧量需要的時間為20天左右，這對實驗室結果，特別是BOD數據用于監(jiān)測水污染處理廠BOD的去除率來說，這個時間太長。It has been found that more than tw

20、o thirds of the BODL is usually exerted within the first 5 d of decomposition. For practical purposes, the 5-d BOD, or BOD5, has been chosen as a representation of the organic content of water or wastewater. For standardization of results, the test must be conducted at a temperature of 20 . In summa

21、ry, the parameter of BOD5 is the amount of dissolved oxygen used by microbes in 5 d to decompose organic substances in water at 20 . 已經發(fā)現超過2/3的BODL在5天之內就被降解。實際應用中，BOD5被用來表示水或者是廢水中的有機物濃度。為了使結果標準化，測定溫度必須為20 ?？傊?，參數BOD5是20 條件下，微生物5天內降解有機物所消耗的溶解氧的數量。4.2 Chemical oxygen demandThere also might be nonbiodeg

22、radable or slowly biodegradable substances that would not be detected by the conventional BOD test. 水中也可能有不可生物降解或者緩慢生物降解的物質，它們不能通過一般的BOD實驗測定出來。The chemical oxygen demand (COD), is another parameter of water quality, which measures all organics including the nonbiodegradable substances. It is a chemi

23、cal test using a strong oxidizing agent, sulfuric acid, and heat. The results of the COD test can be available in just 2 h, a definite advantage over the 5 d required for the standard BOD test. 化學需氧量(或者COD)是另一個水質參數，它包含不可生物降解物質在內的所有有機物。COD的測定是使用一種強氧化劑（重鉻酸鉀），硫酸和加熱的化學試驗。實驗結果只要2 h就可以得到，與標準BOD的測定需要5 d相比，

24、具有明顯的優(yōu)勢。 COD values are always higher than BOD values for the same sample, but there is generally no consistent correlation between the two tests for different wastewaters. 同一樣品的COD值總是比BOD值高，但通常不同廢水兩者之間沒有一致的對應關系。Two of the most common biological treatment systems are the trickling filter and the act

25、ivated sludge process. The trickling is a type of fixed-growth system: the microbes remain fixed or attached to a surface while the wastewater flows over that surface to provide contact with the organics. 兩個最普通的生物處理系統(tǒng)是滴流生物濾池和活性污泥法。滴濾池是一種固定生長系統(tǒng)，即微生物保持固定或者附在一個表面，廢水則流過這個表面使微生物與有機物接觸。4.3 Activated Sludg

26、e TreatmentActivated sludge treatment is characterized as a suspended-growth system because the microbes are thoroughly mixed and suspended in the wastewater rather than (instead of) attached to a particular surface. 活性污泥法的特征是懸浮生長系統(tǒng)，因為微生物與廢水完全混合并懸浮其中，而不是附在一個特殊的表面（載體）上。The basic components of an acti

27、vated sludge sewage treatment system include an aeration tank and a secondary settling basin or clarifier. Primary effluent is mixed with settled solids that are recycled from the secondary clarifier (return sludge) and then introduced into the aeration tank. Compressed air is injected continuously

28、into the mixture through porous diffusers located at the bottom of the tank along one side. This is illustrated in Fig. 2. 活性污泥廢水處理系統(tǒng)的基本組成部分包括曝氣池和二沉池。一級處理的出水與從二沉池回流的流污泥混合，然后進入曝氣池。壓縮空氣不斷地通過位于曝氣池一側底部的多孔擴散器射入混合液。如圖2所示（標準活性污泥處理廠流程圖）。In the aeration tank, microorganisms consume the dissolved organic poll

29、utants as food. The microbes absorb and aerobically decompose the organics, using oxygen provided in the compressed air; water, carbon dioxide, and other stable compounds are formed (Cd).Fig. 2 A flow diagram for a conventional activated sludge plantIn addition to (other than) providing oxygen, the

30、compressed air thoroughly mixes the microbes and wastewater together as it rapidly bubbles up to the surface from the diffusers. 曝氣池中，微生物以溶解的有機污染物為食。微生物吸收并利用壓縮空氣中的氧分解有機物，形成水、二氧化碳和其它穩(wěn)定化合物。除了提供氧氣，當壓縮空氣快速地從擴散器冒出水面時，它還可以使微生物和廢水完全混合。 The aerobic (anaerobic) microorganisms in the tank grow and multiply, f

31、orming an active suspension of biological solids called activated sludge. The combination of the activated sludge and wastewater in the aeration tank is called the mixed liquor. In the basic or conventional activated sludge treatment system, a tank detention time of about 6 h is required for thoroug

32、h stabilization of most of the organics in the mixed liquor. 好氧微生物在曝氣池中生長和繁殖，形成一種稱為活性污泥的活性的生物固體懸浮物。曝氣池中活性污泥和廢水的混合物稱為混合液。基本的或者標準的活性污泥處理系統(tǒng)中，混合液中多數有機物完全穩(wěn)定所需要的水力停留時間大概是6小時。 After about 6 h of aeration, the mixed liquor flows to the secondary or final clarifier, in which the activated sludge solids settl

33、e out by gravity. The clarified water near the surface, called the supernatant, is discharged over an effluent weir; the settled sludge is pumped out from a sludge hopper at the bottom of the tank (Cd). Recycling a portion of the sludge back to the inlet of the aeration tank is an essential characte

34、ristic of this treatment process. 6小時的曝氣后，混合液流入二次或者最后的沉淀池，在那里，活性污泥通過重力沉降。二沉池表面的澄清水叫（也就是上清液）從出水堰排出。沉降污泥用泵從曝氣池底部的污泥斗泵走，（污泥濃縮池），在這種處理方法中，回流一部分污泥至曝氣池的進口是很必要的。The settled sludge is in an active state. In other words, the microbes are well acclimated to the wastewater and, given the opportunity, will read

35、ily absorb and decompose more organics by their metabolism (S). By pumping about 30 percent of the wastewater flow from the bottom of the clarifier back to the head of the aeration tank, the activated sludge process can be maintained continuously (S). 通過從沉淀池低部泵入大約30%的廢水流至曝氣池中，活性污泥處理過程可以連續(xù)不斷的維持。When

36、mixed with the primary effluent, the hungry microbes quickly begin to absorb and metabolize the fresh food in the form of BOD-causing organics. 當回流污泥與一級處理出水混合時，缺乏營養(yǎng)的微生物立即吸收和代謝BOD形式的有機物。Since the microbes multiply and increase greatly in numbers, it is not possible to recycle or return all the sludge

37、 to the aeration tank. The excess sludge, called waste activated sludge, must eventually be treated and disposed of along with sludge from the primary tanks. 由于微生物繁殖和增長很快，因此不可能循環(huán)或者回流所有的污泥至曝氣池中。剩余污泥，也叫廢棄活性污泥，必須和初沉池的污泥一起經過最后的處理和處置。4.4 Sludge settlingIn the activated sludge process, the organic polluta

38、nts are absorbed by the billions of microorganisms in an aeration tank. These microorganisms essentially are the activated sludge. 活性污泥法中，有機污染物在曝氣池中被數十億的微生物吸收。這些微生物本質上是活性污泥。But without proper clarification or separation of the sludge from the liquid portion of the mixed liquor, the treatment process

39、 will not be effective at all. 如果污泥不能適當的從混合液的液體部分澄清或者分離出來，這種處理方法根本就沒有效果。For this reason, gravity settling in the secondary clarifier is a most important part of the activated sludge treatment system. If the sludge does not settle fast enough, some of it will be carried over the effluent weirs of the

40、 clarifier and cause pollution of the receiving body of water (Cx). 因此，（污泥在）二沉池的重力沉降是活性污泥處理系統(tǒng)的一個重要部分。如果不能充分地沉降，有些污泥就會從沉淀池的出水堰流出，導致受納水體的污染。Under certain conditions in an activated sludge sewage treatment plant, filamentous or stringy bacteria grow prolifically in the aeration tank, making the sludge

41、very fluffy and light, sludge with excessive growth of these filamentous organisms settles very slowly, and a clear supernatant is not formed in the secondary clarifier (Cd). 某些情況下，在活性污泥處理廠中，絲狀或者纖維狀的細菌在曝氣池中大量生長，使得污泥變成絨毛似的，很輕，含有過分增長的絲狀微生物的污泥沉降很慢，在二沉池中，不可能形成很清澈的上清液。Much of the sludge flows out with th

42、e effluent, and this condition is called sludge bulking. Bulking of activated sludge may be controlled or limited by appropriate adjustments in the MLSS concentration and F/M ratio; this is accomplished by regulating the rate of sludge return from the clarifier. The amount of aeration may also be a

43、factor; sludge bulking is sometimes associated with too much aeration. Occasionally, adjustments in the mixed liquor pH are made to resolve the problem. 大量的污泥隨液流流出，這種情況叫污泥膨脹?；钚晕勰嗯蛎浛梢酝ㄟ^適當的調整MLSS濃度和F/M比率來控制或者限制。著可以通過調整回流污泥量來完成。曝氣量也是一個因子；污泥膨脹有時與曝氣過量有關。有時，調整混合液的pH也可以解決污泥膨脹問題。A number called the sludge v

44、olume index (SVI) is used to evaluate the settle ability of the activated sludge. It is equal to the volume occupied by 1 g of settled sludge and is expressed in units of mL/g. 污泥體積指數 (SVI) 是用來評估活性污泥的沉降能力的。它等于1克沉降污泥所占（混合液）的體積，單位用毫升每克表示。The determination of SVI involves taking a sample of mixed liquo

45、r from the aeration tank and allowing it to settle for 30 min in a 1-L graduated glass cylinder。SVI的測定是在曝氣池中取樣品于1L的玻璃量筒中，讓它沉降30分鐘。如圖3所示，實驗室測定SVI示意圖。SVI是用來評價污泥的沉降特性的。Fig. 3 Schematic illustration of the lab test for the sludge volume index (SVI), which is used to evaluate sludge settling characteristicsThe volume of settled sludge is read from the markings on the cylinder. The MLSS concentration in the mixed liquor is also measured. The following formula is used to compute/calculate SVI: 沉降污泥的體積從量筒的刻度讀出?；旌弦褐蠱LSS濃度也可以測定出來。SVI的計算可用下式：SVI = (V 1000) / MLSSWhere SVI = sludge v