2024剑桥雅思讲义Reading_Test_4.docx

PaSSage1UsingthesuntopurifywaterThefollowingarticledetailstwomethodsofwaterpurificationbymeansofthesun.Solarwaterdisinfection,alsoknownasSODIS,isamethodOfdisinfectingwaterusingonlysunlightandplasticPETbottles.SODISisafreeandeffectivemethodfordecentralizedwatertreatment,usuallyappliedatthehouseholdlevelandisrecommendedbytheWorldHealthOrganizationasaviablemethodforhouseholdwatertreatmentandsafestorage.SODISisalreadyappliedinnumerousdevelopingcountries.Exposuretosunlightusingthisprocesshasbeenshowntodeactivatediarrhoea-causingorganismsinpolluteddrinkingwater.ForSODISzcolourless,transparentPETwaterorpopbottles(2litreorsmallersize)withfewsurfacescratchesarechosenforuse.Thelabelsareremovedandthebottlesarewashedbeforethefirstuse.Waterfromcontaminatedsourcesispouredintothebottles,and,toimproveoxygensaturation,thebottlesarefilledtothethree-quartermark,shakenfor20seconds(withthecapon),thenfilledcompletelyandrecapped.Verycloudywaterwithaturbidityhigherthan30NTUmustbefilteredpriortoexposuretothesunlight.Thefilledbottlesarethenexposedtothesun.Thebottlesheatfasterandtohighertemperaturesiftheyareplacedonaslopedsun-facingcorrugatedmetalroofascomparedtothatchedroofs.Thetreatedwatercanbeconsumeddirectlyfromthebottleorpouredintocleandrinkingcups.Theriskofre-contaminationisminimizedifthewaterisstoredinthebottleszandrefillingandstorageinothercontainersincreasestheriskofcontamination.Thesecondmethodistouseasolarstill.AsolarstillisasimplewayofdistillingWaterZusingtheheatofthesuntodriveevaporationfromhumidsoil,andambientairtocoolacondenserfilm.Twobasictypesofsolarstillsareboxandpitstills.Inapitsolarstill,apitisduginthegroundandapieceoftransparentplasticissuspendedbetweenlargerockslocatedontheupperedgesofthepit.Asmallweightisplacedontopoftheplasticsheetinthemiddlesoastoweighthesheetdown.Aburiedcupispositionedimmediatelybelowthisweight,beneaththeplastic,atthelowestpointofthepit,andatuberunsfromtheburiedcupbackuptothegroundsurfacesothatwatercanberemovedafterwards.Thewayitworksisthatimpurewaterinthehumidsoiloutsidetheburiedcupisevaporatedbysunlightshiningthroughclearplastic.Thepurewatervapourcondensesonthecoolinsideplasticsurfaceanddripsdownfromtheweightedlowpoint,whereitcollectsintheburiedcupandisthenremovedusingthetube.Thebasicprinciplesofsolarwaterdistillationaresimpleyeteffective,asdistillationreplicatesthewaynaturemakesrain.Thesun'senergyheatswatertothepointofevaporation.Asthewaterevaporates,watervaporrises,condensingontheplasticsurfaceforcollection.Thisprocessremovesimpuritiessuchassaltsandheavymetalsaswellaseliminatingmicrobiologicalorganisms.Theendresultiswatercleanerthanthepurestrainwater.Solarstillsareusedincaseswhererain,piped,orwellwaterisimpractical,suchasinremotehomesorduringpoweroutages.InFloridaandotherhurricanetargetareasthatfrequentlylosepowerforafewdays,solardistillationcanprovideanalternatesourceofcleanwater.Solarstillsareoccasionallyusedonalongertermbasisindevelopingworldsettings.However;dependingonenvironmentalconditions,theyusuallyproducearelativelysmallamountofwater;andevenlesswherethesourceissalineorbrackish.Ifthesourceisinadequate,acompromisemethodistomixthedistilledwaterwiththebrackishorsalinewaterpurifiedwithothermethodsasthisgivesamoreadequatequantityandre-introducestheothersourcecontaminants,whilestillloweringthesalinity,andimprovingthetaste.Knowinghowtoputtogetherasolarstillcanprovetobeausefulsurvivalskillandcouldprovideanimportantmeansofobtainingpotablewaterintheeventofawildernessemergency.Nevertheless,undertypicalconditionsmakeshiftsolarstillsrarelyproduceenoughwaterforlong-termsurvival,andthesweatexpendedinbuildingonecaneasilyexceeditsdailyoutput.Solarstillscanextractwaterfrommoistureinthegroundbuttoincreasetheamountofmoistureavailabletoasolarstill,water(freshorsaline)canbeaddedinsideoralongtheedgesofthestill.Wherenowatersourcesarereadilyavailable,shreddedvegetation,wetsoilorsand,orurineorcoveredfaeces,canbeusedinsidethepit.Ifonlythenaturalsoilmoistureisused,thepitmusteventuallybemovedastheproductivitydrops.Adaptedfrom:https:en.WikiboOkS.orqWiki/DrinkinqWater/Disinfection/SOIarandhttps:en.WikiboOkS.orqWiki/DrinkinqWClter/DistillationQuestions1-4ChoosetheappropriatelettersA,B,CorD.Writeyouranswersinboxes1-4onyouranswersheet.1. SODISA. isseldomusedinthedevelopingworld.B. istypicallymadeuseofindomesticsettings.C. isusedtomeltandrecycleplasticPETbottles.D. canbeexpensive.2. ThePETbottlesusedinSODISA. mustbefilledtothetopbeforetheprocessbegins.B. shouldhaveatleasta2-litrecapacity.C. shouldbepositionedonaslantingmetalsurfacetogetthebestresults.D. musthaveahighturbidityindex.3. AsolarstillA. makesuseofthesameprocessthatisusedtoproduceraininnature.B. requirestheuseofsalttopurifymetals.C. involvesthecollectionofimpurerainwaterinaburiedcup.D. isawayofmeltingandrecyclingclearplastic.4. SolarstillsA. areoftenusedincombinationwithwells.B. canbeimpracticalinhurricanes.C. donotprovidemuchwaterinsalineconditions.D. areuncommoninFlorida.Questions5-9