水污染-英文版

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1、Water pollutionnIt covers 71%of the earths surface and makes up 65%of our bodies.nWithout the seemingly invaluable compound comprised of hydrogen and oxygen,life on Earth would be non-existent Water is Essential for Life nThree fourths of the surface of the Earth is covered with water.Nearly 98%of t

2、he water on Earth,though,is seawater unfit 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 PropertiesnMany chemical substances are soluble in water.Thus,they

3、are 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 nRainwater carries dust particles from the atmosphere to the ground.Rainwa

4、ter 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.nAs water moves along or beneath the surface of the Earth,it dissolves minerals and matter from d

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

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

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

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

9、utionnThe 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.nThere are two sorts of sources,point and nonpoint sources.Point sources discharge pollutants at specific locations through pipelines or sewe

10、rs 下水道into the surface water.Nonpoint sources 非点(污染)源are sources that cannot be traced to a single site of discharge.nFactories nAgriculture nTransportation nHousehold Sources of water pollutionDomestic sewagenDomestic sewage refers to waste water that is discarded from households.Also referred to a

11、s sanitary sewage.nDomestic 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 ChemicalsExample:substances used for houses clean:nSoap and synthetic

12、detergentsnWaxnPaints and paint removersnBleachesnDisinfectants消毒剂nPolishesAgricultural Run off nFertilizers:nitrate,phosphates nPesticides:phenol,chlorine diphenyl nEutrophication富富营养作用营养作用:nutrients artificially supplemented results in an abnormal increase in the growth of water plants Industrial

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

14、chemicals.nExample:Chrome plating on bumpers,grills,and ornaments is a source of pollution Pollutants from various industries nThe textile industry dumps conditioners,dyes,bleaches,and water effluents containing oils,dirt,and other organic debris.nMeat-packing plants dump blood,the contents of entra

15、ils 内脏,and other animal wastes.nOther food-processing plants discharge fruit and vegetable skins,seeds,leaves,stems,and other vegetable wastes.nRefineries 精炼厂 release dyes,oils,acids 盐水,sulfur compounds,and other wastes.nChemicals plants produce a variety of waste materials.Oil spillsnOil spills fro

16、m tankers at sea or leaks from underground storage tanks on land are very difficult to control nOil spills at sea decrease the oxygen level in the water and cause grave harm to the creatures living in the sea.nOn land crude is transported through pipelines or tankers which can get damaged and spew o

17、ut crude oil over the land Oil 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 contaminationnGroundwater are contaminated with heavy metals,persistent organic pollutants,and nutrients nPesticides:Run-off from farms

18、,backyards,and golf coursesnLeachate沥出液from landfill sites nUntreated or inadequately treated municipal sewage:organic material,microbial pathogen nNutrients:phosphorus and nitrogena.Synthetic organics:industrial chemicals and pesticides Chemicals in drinking waternChemicals in drinking water can be

19、 both naturally occurring or introduced by human interference nFluoride nArsenicnPetrochemicalsnChlorinated solvents a.SaltsDifferent types of water pollutionnMicrobiological:Disease-causing(pathogenic)microorganisms,like bacteria,viruses and protozoa原生动物.nChemicals:A whole variety of chemicals from

20、 industry,such as metals,solvents and acids nOxygen-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 bacterianAerobic bacteri

21、a that live in water use oxygen gas dissolved in the water when they consume their food nAerobic 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 carb

22、onates Anaerobic bacterianOnce the oxygen is depleted,other(anaerobic)bacteria that do not need dissolved oxygen take over nAnaerobic microorganisms produce toxic and smelly ammonia,amines,and sulfides,and flammable methane(swamp gas)Biochemical oxygen demand,or BOD nBOD is the amount of oxygen requ

23、ired by micro-organisms to decompose the organic substances in sewage.n The more organic material there is in the sewage,the higher the BOD.Nutrients nWater-soluble nitrates and phosphates that cause excessive growth of algae and other water plants,which deplete the waters oxygen supply.Suspended ma

24、tter nParticulate matter,consist of much larger-but still very small-particles which are just suspended in the watern They will eventually settle out and form silt or mud at the bottom:sediments Water-borne diseasenPathogens which include virus,bacteria,protozoa,and parasitic worms are disease-produ

25、cing agents found in the faeces of infected persons.nHepatitis 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?n In urban areas,the wastewater from homes,businesses and factories is collected by a system of undergro

26、und pipes-sewers which carry it to one or more central treatment facilities.nHomes 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 plantsnConsists of a train of individual unit processes,with the output(ef

27、fluent)of one process becoming the input(influent)of the next process.nBiological plants are more commonly used to treat domestic or combined domestic and industrial wastewater from a municipality.nPhysical/chemical plants are more often used to treat industrial wastewaters directly,because they oft

28、en contain pollutants which cannot be removed efficiently by microorganisms A typical treatment plant nThe first stages will be made up of physical processes that take out easily removable pollutants.nThe remaining pollutants are generally treated further by biological or chemical processes physical

29、 processnA physical process usually treats suspended,rather than dissolved pollutantsnflocculation nFiltration:Ultrafiltration,and reverse osmosis nadsorption on activated charcoal a.Air or steam stripping Desalination of seawater by reverse osmosis.A common set of processes nPreliminary treatment:g

30、rinders,bar screens,and grit channels.nTo remove large or hard solids that might clog or damage other equipment.Primary settling basins n 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 nto remove the remaining

31、dissolved or colloidal organic matter using usually biological method.nThe most common type of biological treatment process:Activated sludge processActivated sludge processnconsists of two parts,an aeration tank and a settling tank.nThe aeration tank contains a sludge:containing mostly bacteria,as w

32、ell as protozoa,fungi,algae,etc.The wastewater enters the tank 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.nThe sludge is carried by the flow into the settling tank.The sludge c

33、ollected at the bottom of the settling tank is then recycled to the aeration tank to consume more organic material.nSince 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 disposalFinal process:Disinfection

34、 nDestruction of harmful(pathogenic)microorganisms,i.e.disease-causing germs:sterilization nThe most commonly used disinfectant is chlorine,in the form of a liquefied gas,or an alkaline solution called sodium hypochloritenA more powerful disinfectant is ozone nThe other commonly used method of disinfection is ultraviolet light