水污染-英文版复习进程

1、水污染-英文版nThree fourths of the surface of the Earth is covered with water. Nearly 98% of the 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

2、 fresh water. Water: Unusual PropertiesnMany chemical substances are soluble in water. Thus, they 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. N

3、atural Water Isnt All H2O nRainwater carries dust particles from the atmosphere to the ground. Rainwater 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 ni

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

5、 negative ions (anions) are usually sulfate (SO42-), bicarbonate (HCO3-), and chloride (Cl-). hard waternWater containing these calcium, 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

6、looking. Water pollution nWater pollution is any chemical, physical or biological change in the quality of water that has a harmful effect 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 groundwater

7、nPollutants in water include a wide of chemicals, pathogens 病原体, and physical chemistry or sensory changes. Water pollutionnWater pollution is 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

8、poisonous drinking water, poisonous food animals, unbalanced river and lake ecosystems, deforestation and many other effects Sources of water pollutionnThe used water of a community is called wastewater, or sewage. If it is not treated before being discharged into waterways, serious pollution is the

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

10、portation nHousehold Sources of water pollutionDomestic sewagenDomestic sewage refers to waste water that is discarded from households. Also referred to as sanitary sewage.nDomestic sewage contains a wide variety of dissolved and suspended impurities: a. organic materials-food and vegetable waste b.

11、 plant nutrients- chemical soaps, washing powders c. disease-causing microbes微生物Household ChemicalsExample: substances used for houses clean:nSoap and synthetic detergentsnWaxnPaints and paint removersnBleachesnDisinfectants消毒剂nPolishesAgricultural Run off nFertilizers: nitrate , phosphates nPestici

12、des: 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 PollutionnIndustrial effluent of many kinds of waste, is discharged into streams, lakes, or oceans, which in turn disperse the pollut

13、ing 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 petrochemicals.nExample: Chrome plating on bumpers, grills, and ornaments is a source of pollution Pollutants from various in

14、dustries 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 entrails 内脏, and other animal wastes. nOther food-processing plants discharge fruit and vegetable skins, seeds, lea

15、ves, 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 from tankers at sea or leaks from underground storage tanks on land are very difficult to control nO

16、il 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 out crude oil over the land Oil spills are very difficult to control as oil tends to spread very

17、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, backyards, and golf coursesnLeachate沥出液from landfill sites nUntreated or inadequately tr

18、eated 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 both naturally occurring or introduced by human interference nFluoride nArsenicnPe

19、trochemicalsnChlorinated 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 industry, such as metals, solvents and acids nOxygen-depleting Substances

20、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 bacteria that live in water use oxygen gas dissolved in the water when they co

21、nsume 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 carbonates Anaerobic bacterianOnce the oxygen is depleted, other (ana

22、erobic) 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 required by micro-organisms to decompose the organic substan

23、ces 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 matter nParticulate matter, consist of much larger- bu

24、t 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-producing agents found in the faeces of infected p

25、ersons. 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 underground pipes- sewers which carry it to

26、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 (effluent) of one process becoming

27、 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 often contain pollutants which

28、 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 processnA physical proces

29、s 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 : grinders, bar screens,

30、 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 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 bacter