1、Unit 13 Text：Water Treatment Processes,自来水处理过程,One of the great achievements of modern technology has been to drastically reduce the incidence of waterborne of diseases such as cholera and typhoid fever.现代化技术所取得的伟大成就之一就是极大的降低了霍乱和伤寒等水源性疾病的发生。 These diseases are no longer the great risks to pubic heal
2、th that they once were. 这些疾病曾经对人类的健康产生过巨大威胁，但现在不是了。 The key to this advance was the recognition that contamination of pubic ware, supplies by human wastes was the main source of infection，and that it could be eliminated by more effective water treatment and better waste disposal. 进步的关键在于人们认识到被人为污染的公
3、共水供应是主要的传染源，这可以通过更积极更先进的水处理技术所消除。,Todays water treatment plants are designed to provide water continuously that meets drinking water standards at the tap. 今天的水处理厂被设计为能持续的提供符合饮用水标准的水。 There are four man considerations involved in accomplishing this：sour selection, protection of water quality，treatmen
4、t methods to be used，and prevention of recontamination. 有四个主要的方面要考虑：水源的选择、水质的保护、所使用的处理方法和如何防止二次污染。 Common precautions to prevent groundwater and surface water pollution include prohibiting the discharge of sanitary and storm sewers close to the water reservoir, installing fences to prevent pollution
5、 from recreational uses of water, and restrictions on the application of fertilizers and pesticides in areas that drain to the reservoir. 一般的预防地下水污染和地表水污染的措施包括防止排泄物管道和雨水管道的排放口靠近蓄水池，安装栅栏防止娱乐用水的污染，限制在水库流域使用化肥和杀虫剂。,Screening，coagulation/flocculation，sedimentation, filtration，and disinfection are the ma
6、in unit operations involved in the treatment of surface water. 隔离、混凝/絮凝、沉淀、过滤是地表水处理的四个主要步骤。Water treatment operations fulfill one or more of three key tasks: removal of particulate substances such. as sand and clay，organic matter, bacteria，and algae；removal of dissolved substances such as those sing
7、 color and.Hardness; and removal or destruction of pathogenic bacteria and viruses. 水处理要实现一到三个目标：去除沙和尘土等颗粒物质、有机物质、微生物和藻类；去除引起色度和硬度的溶解物质；去除或破坏致病细菌和病毒。,The actual selection of treatment processes depends on the type of water source and the desired water quality. 实际的处理工艺的选择有赖于水源的类型和所需要的水质。 Occasionally
8、，raw water with low turbidity can be treated by plain sedimentation (no chemicals) to remove larger particles and then filtration to remove the few particles that failed to settle out. 有时，不太混浊的进水可以通过自然沉降来去除较大的颗粒，在利用过滤去除剩余的颗粒。 Usually, however, particles in the raw water are too small to be removed i
9、n a reasonably short time through sedimentation and simple filtration alone. 但通常，进水的颗粒物非常小，在短时间内仅仅依靠沉淀和简单的过滤无法去除。,To remedy this，a chemical is added to coagulate/flocculate the small particles, called colloids, into large ones, which can then be settled out in sedimentation tanks or removed directly
10、 in filters. 作为补救，将会加入胶体这种化学药品来吸附小颗粒，形成大颗粒在沉淀池里析出，或在过滤池里直接去除。 Removal of Particulate Matter 颗粒物质的去除 The unit operations employed for the removal of particulate matter from water include screening, sedimentation, coagulation/flocculation, and filtration. 从水中去除颗粒物的操作步骤包括隔离、混凝/絮凝、沉淀、过滤。,Screening to re
11、move large solids such as logs，branches, rags，and small fish is the first stage in the treatment of water. 隔离 去除像木屑、树枝、碎布和小鱼这样的大的固体物的隔离过程是水处理的第一步。 Allowing such debris into the treatment plant could damage pumps and clog pipes and channels. 碎片万一进入处理厂可能会损坏水泵，阻塞管道。 For the same reasons，water intakes a
12、re located below the surface of the lake or river in order to exclude floating objects and minimize physical damage from ice. 同样的原因，进水口一般设置在湖面和河水面以下，以免吸入漂浮物，最大程度的减少冰的破坏作用。,Sedimentation，the oldest and most widely used form of water and wastewater treatment uses gravity settling to remove particles f
13、rom water. 沉降是水和废水处理中使用最古老最广泛的处理方式，它是利用重力作用从水中去除颗粒物。It is relatively simple and inexpensive and can be implemented in basins that are round，square，or rectangular. 它工艺相对简单，造价低廉，可以造成圆形、正方形、矩形。 As noted earlier, sedimentation may follow coagulation and flocculation (for highly turbid water) or be omitt
14、ed entirely (with moderately turbid water). 就像前面提到的，对于浊度高的水，沉淀可以放在混凝后面，对于浊度不高的水，则可以完全省去该过程。 Particulates suspended in surface water can range in size from 10- to 10- mm in diameter, the size of fine sand and small clay particles，respectively. 地表水中的悬浮颗粒物的粒径在10-1和10-7毫米之间，分别是细沙和微尘的尺寸。,Turbidity or clo
15、udiness in water is caused by those particles larger than 10-4 mm, while particles smaller than 10- contribute to the waters color and taste. 浊度和不透明度是由那些粒径大于10-4mm的颗粒引起的，小于10-4mm的颗粒主要对色度和臭味有贡献。 Coagulation/flocculation is a chemical-physical procedure whereby particles too small for practical remova
16、l by plain sedimentation are destabilized and clustered together for faster settling 混凝/絮凝 当颗粒太小而用普通沉淀法无法去除时，利用混凝或絮凝的化学-物理过程，就可以让这些颗粒物失去稳定性，凝结成团，从而更快的得到沉降。,A significant percentage of particulates suspended in water are so small that settling to the bottom of a tank would take days or weeks. 水中相当比例的
17、悬浮颗粒物粒径非常小，沉淀到池底需要数天甚至数周。 These colloidal particles would never settle by plain sedimentation. 这些胶体状的颗粒物都不能用普通沉淀法处理。 Coagulation is a chemical process used to destabilize colloidal particles. 混凝是使胶体颗粒失去稳定的一种化学过程。 The exact mechanism is not well understood，but the general idea is to add a chemical wh
18、ich has positively charged colloids to water containing negatively charged colloids. 精确的机理不太好理解，但大体意思就是添加一种含有正电荷胶体的化学药品到含有负电荷胶体的水中。,This will neutralize the negative change on the colloids and thus reduce the tendency for the colloids to repel each other. 这将会中和胶体的负极电荷，并且能够降低胶体互相排斥的趋势。 Rapid mixing f
19、or a few seconds is required to disperse the coagulant. 使混凝剂扩散需要快速搅拌几秒钟。 Gentle mixing, called flocculation, of the suspension is then undertaken to promote particle contact. 轻柔的搅拌，叫做絮凝，悬浮液通过扩大颗粒的接触面。 This is achieved by mechanical mixing through the use of slowly rotating paddles inside the coagula
20、tion/flocculation tank，or by hydraulic mixing which occurs when flow is directed over and around baffles in the tank. 这可以通过机械混合通过使用内置的慢速混凝/絮凝转动桨，或者由液压混合发生在池的挡板周围流动。,Detention time in the coagulation /flocculation tank is usually between 2040 minutes in ranks 34 m deep. 在混凝/絮凝池内停留时间通常是20 - 40分钟，池深有3
21、4m。 Through the combined chemical/physical process of coagulation/flocculation, the colloidal particles which would not settle out by plain sedimentation are agglomerated to form larger solids called floc. 通过结合实际物理/化学混凝过程，胶体粒子，不会通过由普通沉淀出的结块，凝聚成所谓的较大的浮冰固体来出去。 These appear as fluffy growths of irregul
22、ar shape that are able to entrap small noncoagulaed particles when settling downward. 这些显示为不规则形状蓬松生长的有能力吸附沉淀时向下的不易凝聚颗粒。,Aluminum sulfate is the most common coagulant hot organic polymers may also be used alone or in combination with alum to improve flocculation. 硫酸铝是最常见的混凝剂，但有机聚合物也可以单独使用或与明矾一起，改善絮凝效
23、果。 The floc suspension is gently transferred from the coagulation/flocculation tanks to settling tanks, or directly to filters where the floes are removed. 大浮冰悬浮物通常都是从混凝池转移至沉淀池，或当大浮冰去处时可直接转移至过滤器。,Disinfection 消毒 To ensure that water is free of harmful bacteria it is necessary to disinfect it. 为了确保水中
24、没有有害细菌，消毒是很有必要的。 Chlorination is the most common method of disinfecting public water supplies. 氯化消毒是公共供水的消毒最常用的方法。Sufficient quantities of chlorine from chlorine gas or hypochlorites are added to treated water, to kill pathogenic bacteria. 足量的氯气或次氯酸盐添加到水中以杀死致病菌。 Chlorination is a reliable，relatively
25、 inexpensive，and easy disinfection method to use. 氯化是一个可靠的，相对便宜，且易于使用的消毒方法。,Other disinfectants include chloramines，chlorine dioxide，other halogens，ozone，ultraviolet light，and high temperature. 其他消毒剂包括氯胺，二氧化氯，其他卤素，臭氧，紫外线和高温。 Ozonation，which has been used extensively in France，is now gaining acceptan
26、ce in North America，especially as an alternative to prechlorination where natural organics are present. 臭氧氧化,已被广泛地使用法国。目前在北美地区也以获得认可，特别是作为替代在天然有机物存在的地方的预氯化。 Although effective-on, does not leave a lasting residual for long-term disinfection. 虽然有效，但是臭氧不会留下长期持久的残余消毒。,Ozoanation is the disinfection of
27、water by adding ozone，which is a powerful oxidant of inorganic and organic impurities. 臭氧化是向水中添加臭氧的一种消毒方式。臭氧是一种能氧化无机和有机杂质的强氧化剂 。Its advantages over chlorine are that it leaves no tastes or odors，and unlike chlorine，it apparently does nor react with natural organics form compounds hazardous to humans
28、. 相比氯消毒它的优点是，它不会留下味道或气味，与氯气不同的是，臭氧显然不与自然界有机物反应形成有毒化合物来危害人类。,Removal of Dissolved Substances 溶解物质的去除Aeration is used to remove excessive amounts of iron and manganese from groundwater. 曝气是用来清除地下水中过量的铁和锰。These substances cause taste and color problems，interfere with laundering, stain plumbing fixtures
29、, and promote the growth of iron bacteria in water mains. 这些物质引起了味道和颜色的问题，干扰清洗和污染水管装置，并促进铁细菌在水管的繁殖。By bubbling air through water, or by creating contact between air and water by spraying, dissolved iron or manganese (Fe“ Mn“ )is oxidized to a less soluble form(Fe十，Mn*），which precipitates out and can
30、 be removed in a settling tank or filter . 通过向水中鼓泡空气，或者通过喷射来增大空气与水的接触面积，溶解性铁或锰（的Fe2+，Mn2 +）被氧化成一种不易溶解形式（Fe3+，Mn4 +的），这样沉淀出来后可以在沉淀池或过滤器中出去。,Aeration also removes odors caused by hydrogen sulfide (H,S)gas. 曝气也消除了硫化氢（H2S）气体造成的臭味。 Softening of water is a process that removes hardness ,caused by the pres
31、ence of divalent metallic ions principally Ca2+ and Mg2+. 水的软化是一个去除硬度过程，硬度是由二价金属离子的存在造成的，主要是钙离子和镁离子。 Hardness in water is the result of contact with soil and rock，particularly limestone, in the presence of CO2. 水的硬度是在二氧化碳的存在下土壤和岩石，特别是石灰岩接触的结果。,Activated Carbon is an extremely adsorbent material used
32、 in water treatment to remove organic contaminants. 活性炭是一种在水处理中去除有机污染物吸附能力极强的材料。 Activated carbon is produced in a two-stage process. 活性炭的生产有两个阶段。 First, a suitable base material such as wood，peat，vegetable matter，or bone is carbonized by hearing the material in the absence of air. 首先，一个合适的基材如木材、虫、蔬
33、菜等物质或者骨头，在通过隔绝空气的条件下加热使它们碳化。 Then the carbonized material is activated by heating it in the presence of air，CO2 or steam to burn off any tars it has and to increase its pore size. 然后碳化材料在空气，二氧化碳，或蒸汽条件下加热燃烧掉它的杂质后被活化，并增加其孔径。,Adsorption of gases, liquids, and solids by activated carbon is influenced by
34、 the temperature and pH of the water as well as the complexity of the organics being removed. 活性炭对气体，液体和固体的吸附是受温度，水的pH值以及需要除去的有机物的复杂性。 In reverse osmosis (RO）.fresh water is forced through a semi permeable membrane in the direction opposite to that occurring in natural osmosis. 在反渗透（RO）中，淡水强行通过半透膜的方
35、向，是自然渗透的相反方向。 Because the membrane removes dissolved salts，the main application for RO has been in desalination. 由于膜能去除可溶性盐，所以反渗透主要应用在海水淡化。 However，the process also removes organic materials. bacteria. and viruses, and its application in water treatment is growing . 然而，这个处理过程也能去除有机物质，细菌和病毒，其在水处理中的应用越来越大。,
