水污染英文版ppt课件.ppt

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1、Water pollution,It covers 71%of the earths surface and makes up 65%of our bodies.Without the seemingly invaluable compound comprised of hydrogen and oxygen,life on Earth would be non-existent,Water is Essential for Life,Three fourths of the surface of the Earth is covered with water.Nearly 98%of the

2、 water on Earth,though,is seawaterunfit for drinking and not even suitable for most industrial purposes.Something less than 2%of the water is frozen in the polar ice caps,leaving less than 1%available as fresh water.,Water:Unusual Properties,Many chemical substances are soluble in water.Thus,they ar

3、e easily dispersed and eventually are scattered to nearly infinite dilution in the ocean.Those properties of water that make it uniquely suited for the support of life also make it easy to pollute.,Natural Water Isnt All H2O,Rainwater carries dust particles from the atmosphere to the ground.Rainwate

4、r also dissolves a little oxygen,nitrogen,and carbon dioxide as it falls through the atmosphere.During electrical storms,lightning causes nitrogen,oxygen,and water vapor to combine to form nitric acid.,As water moves along or beneath the surface of the Earth,it dissolves minerals and matter from dec

5、aying plants and animals.The principal positive ions(cations)in natural water are sodium(Na+),potassium(K+),calcium(Ca2+),magnesium(Mg2+),and sometimes iron(Fe2+or Fe3+).The negative ions(anions)are usually sulfate(SO42-),bicarbonate(HCO3-),and chloride(Cl-).,hard water,Water containing these calciu

6、m,magnesium,and iron ions is called hard water.The positive ions react with the negative ions in soap to form a scum that clings to clothes and leaves them dingy looking.,Water pollution,Water pollution is any chemical,physical or biological change in the quality of water that has a harmful effect o

7、n any living thingWater pollution caused by human activities is a large set of adverse effects upon water bodies such as lakes,rivers,oceans,and groundwaterPollutants in water include a wide of chemicals,pathogens 病原体,and physical chemistry or sensory changes.,Water pollution,Water pollution is the

8、leading worldwide cause of deaths and diseases,and that it accounts for the deaths of more than 14,000 people daily.Effects of water pollution include poisonous drinking water,poisonous food animals,unbalanced river and lake ecosystems,deforestation and many other effects,Sources of water pollution,

9、The used water of a community is called wastewater,or sewage.If it is not treated before being discharged into waterways,serious pollution is the result.There are two sorts of sources,point and nonpoint sources.Point sources discharge pollutants at specific locations through pipelines or sewers 下水道i

10、nto the surface water.Nonpoint sources 非点(污染)源are sources that cannot be traced to a single site of discharge.,Factories Agriculture Transportation Household,Sources of water pollution,Domestic sewage,Domestic sewage refers to waste water that is discarded from households.Also referred to as sanitar

11、y sewage.Domestic sewage contains a wide variety of dissolved and suspended impurities:a.organic materials-food and vegetable waste b.plant nutrients-chemical soaps,washing powders c.disease-causing microbes微生物,Household Chemicals,Example:substances used for houses clean:Soap and synthetic detergent

12、sWaxPaints and paint removersBleachesDisinfectants消毒剂Polishes,Agricultural Run off,Fertilizers:nitrate,phosphates Pesticides:phenol,chlorine diphenyl Eutrophication富营养作用:nutrients artificially supplemented results in an abnormal increase in the growth of water plants,Industrial Pollution,Industrial

13、effluent of many kinds of waste,is discharged into streams,lakes,or oceans,which in turn disperse the polluting substances.The pollutants include grit,asbestos石棉,phosphates and nitrates,mercury,lead,caustic soda and other sodium compounds,sulfur and sulfuric acid,oils,and petrochemicals.Example:Chro

14、me plating on bumpers,grills,and ornaments is a source of pollution,Pollutants from various industries,The textile industry dumps conditioners,dyes,bleaches,and water effluents containing oils,dirt,and other organic debris.Meat-packing plants dump blood,the contents of entrails 内脏,and other animal w

15、astes.Other food-processing plants discharge fruit and vegetable skins,seeds,leaves,stems,and other vegetable wastes.Refineries 精炼厂 release dyes,oils,acids 盐水,sulfur compounds,and other wastes.Chemicals plants produce a variety of waste materials.,Oil spills,Oil spills from tankers at sea or leaks f

16、rom underground storage tanks on land are very difficult to control Oil spills at sea decrease the oxygen level in the water and cause grave harm to the creatures living in the sea.On land crude is transported through pipelines or tankers which can get damaged and spew out crude oil over the land,Oi

17、l spills are very difficult to control as oil tends to spread very fast,affecting a large area in a very short time.,Groundwater and its contamination,Groundwater are contaminated with heavy metals,persistent organic pollutants,and nutrients Pesticides:Run-off from farms,backyards,and golf coursesLe

18、achate沥出液from landfill sites Untreated or inadequately treated municipal sewage:organic material,microbial pathogen Nutrients:phosphorus and nitrogenSynthetic organics:industrial chemicals and pesticides,Chemicals in drinking water,Chemicals in drinking water can be both naturally occurring or intro

19、duced by human interference Fluoride ArsenicPetrochemicalsChlorinated solvents Salts,Different types of water pollution,Microbiological:Disease-causing(pathogenic)microorganisms,like bacteria,viruses and protozoa原生动物.Chemicals:A whole variety of chemicals from industry,such as metals,solvents and ac

20、ids,Oxygen-depleting Substances Many wastes are biodegradable,they can be broken down and used as food by microorganisms like bacteria.Too much biodegradable material can cause the serious problem of oxygen depletion in waters,Aerobic bacteria,Aerobic bacteria that live in water use oxygen gas disso

21、lved in the water when they consume their food Aerobic microorganisms-which use dissolved oxygen-convert the nitrogen,sulfur,and carbon compounds present in the wastewater into odorless-and relatively harmless-oxygenated forms like nitrates,sulfates and carbonates,Anaerobic bacteria,Once the oxygen

22、is depleted,other(anaerobic)bacteria that do not need dissolved oxygen take over Anaerobic microorganisms produce toxic and smelly ammonia,amines,and sulfides,and flammable methane(swamp gas),Biochemical oxygen demand,or BOD,BOD is the amount of oxygen required by micro-organisms to decompose the or

23、ganic substances in sewage.The more organic material there is in the sewage,the higher the BOD.,Nutrients,Water-soluble nitrates and phosphates that cause excessive growth of algae and other water plants,which deplete the waters oxygen supply.,Suspended matter,Particulate matter,consist of much larg

24、er-but still very small-particles which are just suspended in the water They will eventually settle out and form silt or mud at the bottom:sediments,Water-borne disease,Pathogens which include virus,bacteria,protozoa,and parasitic worms are disease-producing agents found in the faeces of infected pe

25、rsons.Hepatitis 肝炎,cholera霍乱,dysentery痢疾,diarrhoea腹泻,skin irritation,and typhoid伤寒症are common water-borne diseases,How do we prevent water pollution?,In urban areas,the wastewater from homes,businesses and factories is collected by a system of underground pipes-sewers which carry it to one or more c

26、entral treatment facilities.Homes in non-urban areas that are not connected to a sewer are usually required by their town to have on-site treatment systems.,Wastewater treatment plants,Consists of a train of individual unit processes,with the output(effluent)of one process becoming the input(influen

27、t)of the next process.Biological plants are more commonly used to treat domestic or combined domestic and industrial wastewater from a municipality.Physical/chemical plants are more often used to treat industrial wastewaters directly,because they often contain pollutants which cannot be removed effi

28、ciently by microorganisms,A typical treatment plant,The first stages will be made up of physical processes that take out easily removable pollutants.The remaining pollutants are generally treated further by biological or chemical processes,physical process,A physical process usually treats suspended

29、,rather than dissolved pollutantsflocculation Filtration:Ultrafiltration,and reverse osmosis adsorption on activated charcoal Air or steam stripping,Desalination of seawater by reverse osmosis.,A common set of processes,Preliminary treatment:grinders,bar screens,and grit channels.To remove large or

30、hard solids that might clog or damage other equipment.,Primary settling basins,The water flows slowly for up to a few hours,to allow organic suspended matter to settle out or float to the surface.,Secondary treatment,to remove the remaining dissolved or colloidal organic matter using usually biologi

31、cal method.The most common type of biological treatment process:Activated sludge process,Activated sludge process,consists of two parts,an aeration tank and a settling tank.The aeration tank contains a sludge:containing mostly bacteria,as well as protozoa,fungi,algae,etc.The wastewater enters the ta

32、nk and mixes with the culture,which uses the organic compounds for growth-producing more microorganisms-and for respiration,which results mostly carbon dioxide and water.,The sludge is carried by the flow into the settling tank.The sludge collected at the bottom of the settling tank is then recycled

33、 to the aeration tank to consume more organic material.Since the amount of microorganisms,or biomass,increases as a result of this process,some must be removed on a regular basis for further treatment and disposal,Final process:Disinfection,Destruction of harmful(pathogenic)microorganisms,i.e.disease-causing germs:sterilization The most commonly used disinfectant is chlorine,in the form of a liquefied gas,or an alkaline solution called sodium hypochlorite,A more powerful disinfectant is ozone The other commonly used method of disinfection is ultraviolet light,