water pollution.docx

water pollution.docx

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waterpollution

WATERPOLLUTION

1.Introduction.

1.1.Needforwater.

1.2.Locationofwater.

1.3.Hydrologiccycle.（水解）

2.Freshwatercomposition.

3.Freshwaterpollution.

4.Naturalregeneration.

5.Parametersdeterminingwater’scharacteristics.

5.1.Physicalparameters.

5.2.ChemicalsParameters.

5.3.Otherparameters.

6.Legislation.（法律）

6.1.EuropeanCharteronWaterResources.

6.2.SpanishLegislation.

6.3.EuropeanLegislation.

7.Wastewatertreatment.

7.1.Introduction.

7.2.Preliminarytreatment.（初步）

7.3.Primarytreatments.

7.4.Secondarytreatments.

7.5.Tertiary（第三）treatments.

7.6.Effluentdisinfection.（污水消毒）

8.Sludgetreatment.（污泥处理）

8.1.Introduction.

8.2.Concentration.

8.3.Stabilization.

8.4.Mechanicaldewatering（机械脱水）

8.5.Heatdrying.

8.6.Finaldisposal.

9.Examplesofurbanwastewatertreatment

1.Introduction.

Thefourbasicnaturalresourcesarewater,air,landandenergy.Weneedwaterfor

multipleusesandacertainqualityisrequired.Itsuseleadstothegenerationof

wastewaterthatcancauseanimpactontheenvironment.

Waterscarcityandpollutionhasbecomeofmostimportanceinrecentyears.In

thischapterwe’lldiscussbothfreshwaterandwastewatertreatment,eitherforreuseordisposalintheenvironment"withoutpollutingit"

1.1Needforwater.

TheuseofwatercouldbeclassifiedinorderofimportanceasshowninTable1.

Table1.Wateruse.

NeedsWORLDWIDE%EUROPE%

Agriculture6630

Industry2414

Urban818

Others（refrigeration,energy,

recreational,etc.）

238

Let'sseesomeexamplesoftheorderofmagnitudeofwaterconsumption:

Agriculture.

InSpain,waterconsumptioninagriculturemakesup80%,although

withmoderntechniquesofdripirrigation,significantsavingscouldbeachieved.

Forexample,toproduce1metrictonofmaize（玉米）1,000metrictonsofwaterareneeded.

Industry.

Theapplicationsofwaterinindustryarenumerous.

Forexample,toproduce1tonofpaperrequires25metrictonsofwaterandatanning（皮革）factoryconsumesover20Lofwaterperkiloofrawmaterial（原料）

Domesticuses.

InSpaineachhabitantconsumesbetween200and300liters.AnAmericanconsumesabout340litresperday.

Aswecansee,needsforwaterathomeareminimalwhencomparedtotheoverall

amountrequiredbymantocoveralltheirneeds.

InformationaboutwateruseinEuropecanbefoundat

http:

//www.grid.unep.ch/product/publication/freshwater_europe/consumption.php

1.2Locationofwater.

Waterisoneofthemostabundantsubstancesinnature.Itisfoundin:

Livingbeings,asthemainconstituent.

Inmostfoods.

OnEarth.Watercoversnearlythreequartersoftheearth'ssurface,withatotal

volumeofabout1,360106km3.

ItisdistributedasshowninTable2:

Table2.Waterinventory.

ReservoirVolume（cubickm

x1,000,000）

PercentofTotal

Oceans1,37097.25

IceCapsandGlaciers292.05

Groundwater9.50.68

Lakes0.1250.01

SoilMoisture0.0650.005

Atmosphere0.0130.001

StreamsandRivers0.00170.0001

Biosphere0.00060.00004

Thiscouldbeapessimisticinventoryofavailablewater,giventhatnearly98%is

seawater,and,almost80%oftherestisice.However,thisisnotarealpicturebecausethewateravailableforconsumptionisrenewedthroughthewatercycle.

1.3Hydrologiccycle.（水文循环）

Hydrologiccycleistheprocessbywhichtheamountofwaterexistingonearth

remainsconstantandisduetotheconstantexchangeofwaterthattakesplacebetweentheearth'ssurfaceandatmosphere.

Thehydrologiccycleisaconceptualmodel（概念模型）thatdescribesthestorageandmovementofwaterbetweenthebiosphere,atmosphere,lithosphere,（Figure1）,andthehydrosphere.Wateronthisplanetcanbestoredinanyoneofthefollowingreservoirs:

atmosphere,oceans,lakes,rivers,soils,glaciers,snowfields,andgroundwater.

Figure1.Hydrologiccycle.

Table3.Typicalresidencetimesofwaterfoundinvariousreservoirs.

ReservoirAverageResidenceTime

Glaciers20to100years

SeasonalSnowCover2to6months

SoilMoisture1to2months

Groundwater:

Shallow100to200years

Groundwater:

Deep10,000years

Lakes50to100years

Rivers2to6months

2.Freshwatercomposition.

Freshwaterisnotpurebecauseofitshighpowerassolvent（溶剂）.Thus,itcontainsdissolvedgases,suspendedsolids（悬浮固体）anddissolvedsolids.Thesecompoundsareincorporatedduringitsfallasrainandduringitspercolation（过滤）throughthesoil.Inaddition,wateralsoincorporatesmicroorganismsfromairandsoil.Thus,groundwaterpresentsaveryhighdegreeofmineralization,asopposedtosurfacewater.

Table3comparesthecharacteristicsofgroundwaterandsurface.

Table4.Characteristicsofsurfaceandgroundwater

Characteristicssurfacewatergroundwater

Minerals

Dissolvedoxygen

Hydrogensulphide（硫化氢）

Colour

Turbidity

Ironandmanganese

OrganicCompounds

Pollution

Low

Saturated

Absent

Present

Present

Unusual

Variable

Frequent

High

Low

Maybepresent

Notpresent

Notpresent

Frequent

Variable

Unusual

3.Freshwaterpollution.

Freshwaterpollutioniscausedbythedischargesoftoxicsubstancescomingfrom

domestic,industrialandagriculturaluses.Waterpollutantsareclassifiedas:

（污染分类）

•BiodegradableOrganicSubstances.（生物可降解有机物）

Thesearesubstancesthatoxidizeinthepresenceofoxygenduetobacterialactivity.Asaresult,thereisadecreaseintheconcentrationofdissolvedoxygen,whichcauses:

Adverseeffectsonaquaticlife.

Presenceofbadodours.

•Nutrients.

Theseareessentialchemicalelementsforthegrowthoflife.InadditiontocarbonN,P,S,K,Ca,Fe,Mn,CoBarealsoneeded.

Nutrientsbecomepollutantswhentheirconcentrationsaresohighthattheyallowexcessivegrowthofaquaticplants,mainlyalgae.Thisprocessiscalledeutrophicationandismainlyduetoanincreaseinphosphorus.

•Pathogens.（病原体）

Thoseorganismsabletoproducediseases.

Examplesofpathogensassociatedwithwaterareviruses,bacteria,protozoa（原生动物）andhelminths.蠕虫

•Salinity.

Theamountofdissolvedsaltslimitsthepossibleusesofwater.Itisnormallyduetothepresenceofchloride（氯化物）.Waterisbrackishwhenchloridecontentisgreaterthan5,000ppm.Chloridecontentindrinkingwatermustbelessthan500ppm.

•Heavymetals.

Amongtheheavymetalsare:

Al,As,Be,Bi,Cd,Zn,Co,Cu,Cr,Sn,Fe,Mn,Hg,Ni,Pb,Se,Tl,Ti.Someofthemarenutrientsformanyanimalsandplants,butingreaterconcentrationstheyaretoxic.

Onecharacteristicofmetalpollutionisitspersistenceintheenvironment.Inaddition,heavymetalsconcentratealongthefoodchain.

•Minororganiccompounds.（微量有机化合物）

Thesecompoundsarefoundinalesserconcentrationandcomefromplastics,fuels,solvents,paints,pesticides,detergents,foodadditives,pharmaceuticals,etc.Usuallythesecompoundsarehardlybiodegradableornon-biodegradable.

•Radioactivesubstances.

Producedduringtheproductionanduseofuranium.However,someoftheradioactiveelementsfoundinwaterareofnaturalorigin.

•Thermalpollution.

Itisduetotheuseofwaterascoolant（冷却剂）inmanyindustrialprocesses,whenalargepartofthewaterreturnedtoitsnaturalsourcereturnsseveraldegreeswarmer.Incrementoftemperaturecausesthefollowingeffects:

Reduceoxygensolubilityinwater.

Increasemetabolicreactionsspeed.（代谢反应）

•Sediments.（沉淀物）

Thesearemixturesofmud,sand,organicmatterandvariousminerals,thatappearasaresultoferosion（腐蚀）anddomesticandindustrialdischarges.

Harmfuleffectsofsedimentsare:

Reducethecapacityoflakesandreservoirs.

Affectthebottom-dwellerlife.

Produceturbidity.

4.Naturalregeneration.（自然重建）

Whenadischargeofdomesticwastewatertoariveroccurs,microorganismsuseorganicmaterialtoobtainenergythroughoxidationwiththedissolvedoxygeninwater（catabolism分解代谢）,aswellastoconstructcell-matter（anabolism合成代谢）.

Thiswillcausetheeliminationoforganicmatter有机物andareductionofO2concentrationinwater.Asavailablefoodsourcesdiminish减少,thedeathofmicroorganismsanddestructionofcell-materialisproduced.Atthesametime,oxygenconcentrationincreasesduetoitsdiffusionfromatmosphere.Attheendofthisprocess,downstream,thesituationgoesbacktoitsinitialstate,throughanaturalregenerationprocess.However,thecapacityforthisnaturalregenerationislimited,sothatwastewatershouldbetreatedbeforebeingdischarged.

5.Parametersdeterminingwater’scharacteristics.

5.1Physicalparameters.

•Temperature.

Itismeasuredeasilyandisveryimportantinordertoassessthespeedofbiochemicalreactionsoforganicmatterdecomposition有机物溶解,thesolubilityofgasesoramplificationofflavorsandodours.

•Color.

Itisduetothepresenceoforganicandinorganicmaterialsinwater.Truecolorisduetodissolvedmaterialsandapparentcolorisduetosuspendedmaterials.Colorisusuallymeasuredbycomparisonwithcoloredpatterns.

•Turbidity.

Wateriscloudywhenitcontainsmaterialorcolloidalsuspension.

Turbiditycanbedeterminedbythesemethods:

a）Turbidimetry:

Comparingthetransmissionofwhitelightthroughthesuspensionandthroughastandarizedsolution.

b）Nephelometry.Comparingtheintensityoflightscatteredinthesampleandinareferencedissolution.Thismethodisbroadlyusedandcanbecarriedoutcontinuouslyandisrelatedtosuspendedsolids.

Figure2.Equipmentforturbiditydetermination.

•Solids:

Totalsolidsrefertotheresidueremainingafteraprocessofevaporationat

103-105°C.

Solidscanbeclassifiedaccordingtodifferentcriteria:

a）Dependingontheirnature.

Organic.Thesearesubstancesofanimalorvegetalorigin