专业外语教材Word文档下载推荐.docx

专业外语教材Word文档下载推荐.docx

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一、BasicFactorsinWaterAnalysis

Colour

1Colourisduetothepresenceofcolloidalorganicmatterinsolutionorinsuspension.Thereisnorelationbetweenthecolourandthequantityoforganicmatter,　asthelattermaybecolouredornot.

2Waterwhichiscolouredisunpleasantwhenusedfordomesticpurposes,　andparticularlyfordrinking,aditalwaysgivesrisetodoubtsregardingitsportability.　Certainindustriesrequirewatertobequitefreefromcolourwhichmightaffecttheproductsmanufacturedanddetractfromtheirquality;

　examplesarethepaper,rayon,cellulose,　starch,　anddyeingindustries.Colourremovaliseffectedbycoagulation.

OdourandTaste

Odoursandtastesaregenerallycausedbythepresenceofsecretionsintroducedintothewaterbyorganismswhichliveinthewater,suchasalgaeandfungi,　etc.Certainchemicalproductsinsmallquantitiesalsogiveoffunpleasantodours.Thisisthecasewithphenolswhich,whencombinedwithchlorine,　formtheverymalodorouschlorophenols.Unpleasanttastesarenotconsideredtobeimportantfromthehealthpointofview,　buttheyareextremelyobjectionableindrinkingwater.

Unpleasanttastesarecombatedbybreak-pointchlorination,byactivatedcarbon,bychlorinedioxide,andbyozone.Allwatersamples,fromwhateversource,havetheirownparticulartasterduetothesaltsandgasesdissolvedinthem.

Turbidity

Turbiditygivesanideaofthecontentofmatterinsuspension.Theturbiditymaybeexpressedintermsofsilicabycomparingitstransparencywithanartificialsuspensionofsilica.Itexpressestheconcentrationoffinelydividedsuspendedmatterwhichmayeventuallysettleafervariableperiodsoftime,suchsubstancesbeingclay,finesand,limestoneparticles,etc.Themeasurementofturbiditybydropsofmasticisparticularlyusefulinascertainingthecontentofthecolloidalparticleswhichwillnotsettleandwhichcannotbefiltered.Thatiswhyitisessentialtocarryoutthistestafterfilteringtheliquidthroughpaperinordertoeliminatetheinfluenceoflargeparticles,andthustoknowexactlytheextentoftheturbidityduetothecolloidalsubstanceswhicharethemostfrequentcausesofcolour.

Turbidityisalwaysunpleasantindrinkingwater.

Waterscontainingsuspendedmatterwhichmayeventuallysettlealwayscausedifficultyduetotheformationofdepositsinpipesandtanks.

Lastly,industriesinwhichthewatercomesintocontactwiththemanufacturedproductsalwaysdemandclearwaterwhileoftenpermittingacertaincolloidalturbidity.

Turbidityisrelatedtotransparency.

Aturbidityvalueoflessthan10dropsofmasticgivesgoodtransparencythroughadepthof4metresbutdrinkingwatersgenerallyrequireaturbidityvalueoflessthan4drops.

Colloidalturbiditycanbeeliminatedonlybycoagulation.

Asageneralrulethewaterisclarifiedinasettlingtankwithorwithoutcoagulation,andthisprocessisfollowedbyfiltration.

Watercontaininglessthan20p.p.m.ofsuspendedmatterwhichcanbecoalescedanddecolorizedbytheuseofnotmorethan20p.p.m.ofcoagulantcanbetreatedbydirectfiltration.

Knowledgeofturbidityisanindispensablefactorinwatertreatment.

ConductivityorResistivity

Conductivitydependsontheconcentrationofdissolvedsolid.Itsmeasurement,whichisquiteaneasymatter,givessomeideaastothesaltconcentrationinthewater.Knowledgeofthisfactorisparticularlyusefulfortheperiodiccheckingofagivenwater,asimmediateindicationofvariationsincompositionisobtained.

Temperature

Thetestfortemperatureofwaterhasnopracticalmeaninginthesensethatitisnotpossibletogiveanytreatmenttocontrolthetemperatureinanywatersupplyproject.Thetemperatureofwatertobesuppliedfromstoragereservoirdependsonthedepthfromwhichitisdrawn.Thedesirabletemperatureofpotablewaterif10℃whichtemperatureof25℃isconsideredtobeobjectionable.

Itshouldhoweverbenotedthatchangesintemperatureofwaterfromitssourcetothemainsmaybehelpfulindetectingtheunsuspectedsourceofpollution.Also,themultiplicationofbacteriainthewatersismorerapidathighertemperaturethaninthewatersatlowertemperature.Hencewhenwaterswithatemperatureofabout15℃arecollectedforbacteriologicalanalysis,theyshouldbecooleddownasquicklyaspossible.Itshouldfurtherberememberedthattheairtemperatureatthetimeoftakingthewatersampleshouldalwaysberecorded.

PHValue

PHvaluesindicatewhetherthewaterisacidoralkaline.Phvalueslessthan7showatendencytowardsacidity.Valuesabove7indicateatendencytowardsalkalinity.

Theyhavenohealthsignificance,butrepresentaveryimportantfactorindeterminingthecorrosiveactionofawater.

TheregularmeasurementofthePhvalueisanessentialfactorinwatertreatmentpractice.Inparticularitplaysanimportantpartintheefficiencyofthecoagulationprocess.

二、Water-supplyEngineering

Awatersupplyforatownusuallyincludesastoragereservoiratthesourceofthesupply,apipelinefromthestoragereservoirtothedistributionreservoirnearthetown,andfinallythedistributionpipesburiedinthestreets,takingthewatertothehouses,shops,factoriesandoffices.Themainequipmentisthusthetworeservoirsandthepipelinebetweenthem.Thefunctionofthestoragereservoiriskeepingenoughwateroveroneorseveralyearstoprovideforallhighdemandsindryperiods,andthedistributionreservoirhasthesamefunctionforthedayortheweek.Thestoragereservoirsimilarlyallowsthepipelineandpumpstobesmallerandcheaperthantheywouldbeifitdidnotexist.

IntheUnitedStates,someofwhosecitieshavethelargestwateruseintheworldperperson,theaverageuseperpersonvariesform200to5000litresperday,averagingsome500litres/day/person.Butitmustnotbeassumedthatcoldercountrieswilleventuallyreachthesamelevelofuse,becausemuchofthehighestUSdemandcomesfromthewaterspentinsummeronairconditioningequipmentandthewateringofgardens.

Waterengineersmustthereforestudythewateruseperperson（consumptionperhead）intheirowncountryandchooseafigurebasedonthemostadvancedcommunitythere.Thechosenconsumptionperheadmustbemultipliedbytheestimatedpopulationatthedateforwhichthesupplyisbeingplanned,somethirtyyearsaheadormore.Thesupplyandstorageequipmentmustbedesignedtobelargeenoughforthisperiodsinceneitherofthemissoeasilyextendedasthedistributionsystem.Thiscanbeextendedastheneedarisesandasthehousesarebuilt.

Oncethevolumeoftherequiredyearlysupplyhasbeencalculatedandagreedwithallconcerned,includingthefiredepartment,itisimportanttomakesurethatitreallyispermanentlyobtainablefromthecatchmentareaproposed.Thecatchmentareaistheareawhichdrainstowardsthesupply,andtheyearlyamountofwaterdrawnofftothestoragereservoircannotbemorethantherainfallonthecatchmentareaandshouldusuallybeverymuchsmaller.

Awatersupplymaybeobtainedfromsurfacewater（rain）orfromundergroundwaterorboth.Botharerefilledbytherainfall,thesurfacewaterbytherunoff,andthespringsorwellsbythewaterwhichenterstheground,theinfiltrationwater.Thesetwoquantities,plustheevaporationwaterandthewaterusedbythetreesandplants,makeupthetotalrainfall.Evenifthecommunitywatersupplyincludesallthespringsaswellasthesurfacewaterinthearea,itstilldoesnotobtainalltherainfallbecauseofevaporationandtheneedsofplantlife.

Itisthereforeimportanttochecktherainfallrecordsandrunoffandinfiltrationvalueswiththerecordsofthestreamflowsandotherlocalwaterinformation.Infiltrationwater,therainfallwhichentersthegroundandbecomesgroundwater,cantravelforlonghorizontaldistances,anditmaypassintooroutofthecatchmentarea.Iftheyearlywatersupplyexceedstheyearlyrainfall,thegroundwaterlevelwillgenerallyfallandeventuallyitwillbecomeimpossibletoobtaintherequiredsupply.Anothersourcewillhavetobefound.

Itisnotessentialtobuildastorageorimpoundingreservoirifthewatercanbestoredintheground,andthismayoftenbepossible.InfactintheLondonarea,wherethewaterlevelinthechalkhasbeensteadilyfailingformorethanacenturybecauseofpumping,ithasbeensuggestedthatfurtherstorageshallbenotbythesurfacereservoirswhichhavebeenuseduntilnow,butbyrechargingthechalkwithpurifiedwaterthroughwellschangedforthepurpose.

Thispracticeofundergroundstorageisbeingwidelyusedbythegasindustryinmanycountries.Gasissentundergroundbycompressorsthroughwellsintoasealedundergroundsand,limestone,orotherporousformationatatimewhenthegassupplyislarge,tobestoreduntilthedemandislargerthanthesupply.Theseundergroundcontainersforgasareoftenhundredsoftimesaslargeasthelargestgastankinexistenceandhavebeenfoundtobeacheap,practical,andsafewayofstronggas.

三、ThePurificationofWater

1.Seawatercanbeusedforasupplyofpotable（ordrinkable）waterifitcanbeseparatedfromthesaltdissolvedinit.Themostdirectwaytodothisistodistilit---turnitintosteam,andthencondensethesteam.Inthepast,distillationhasalwaysbeentooexpensive,butagreatdealofsuccessincheapeningtheprocesshasbeenachievedinthelastfewyears.Somecleverideashavebeenthoughtouttodothis.

2.Anothermethodofgettingridofsaltisbyelectro-dialysis.Thisisanelectricalmethodwhichismostpromisin