单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,*,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 health 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，treatment 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C,ommon 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 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 main 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 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，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 in 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 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 remove 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 are 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 from 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 omitted 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 cloudiness 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 removal 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Coagula。