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1、PaSSage1UsingthesuntopurifywaterThefollowingarticledetailstwomethodsofwaterpurificationbymeansofthesun.Solarwaterdisinfection,alsoknownasSODIS,isamethodOfdisinfectingwaterusingonlysunlightandplasticPETbottles.SODISisafreeandeffectivemethodfordecentralizedwatertreatment,usuallyappliedatthehouseholdle
2、velandisrecommendedbytheWorldHealthOrganizationasaviablemethodforhouseholdwatertreatmentandsafestorage.SODISisalreadyappliedinnumerousdevelopingcountries.Exposuretosunlightusingthisprocesshasbeenshowntodeactivatediarrhoea-causingorganismsinpolluteddrinkingwater.ForSODISzcolourless,transparentPETwate
3、rorpopbottles(2litreorsmallersize)withfewsurfacescratchesarechosenforuse.Thelabelsareremovedandthebottlesarewashedbeforethefirstuse.Waterfromcontaminatedsourcesispouredintothebottles,and,toimproveoxygensaturation,thebottlesarefilledtothethree-quartermark,shakenfor20seconds(withthecapon),thenfilledco
4、mpletelyandrecapped.Verycloudywaterwithaturbidityhigherthan30NTUmustbefilteredpriortoexposuretothesunlight.Thefilledbottlesarethenexposedtothesun.Thebottlesheatfasterandtohighertemperaturesiftheyareplacedonaslopedsun-facingcorrugatedmetalroofascomparedtothatchedroofs.Thetreatedwatercanbeconsumeddire
5、ctlyfromthebottleorpouredintocleandrinkingcups.Theriskofre-contaminationisminimizedifthewaterisstoredinthebottleszandrefillingandstorageinothercontainersincreasestheriskofcontamination.Thesecondmethodistouseasolarstill.AsolarstillisasimplewayofdistillingWaterZusingtheheatofthesuntodriveevaporationfr
6、omhumidsoil,andambientairtocoolacondenserfilm.Twobasictypesofsolarstillsareboxandpitstills.Inapitsolarstill,apitisduginthegroundandapieceoftransparentplasticissuspendedbetweenlargerockslocatedontheupperedgesofthepit.Asmallweightisplacedontopoftheplasticsheetinthemiddlesoastoweighthesheetdown.Aburied
7、cupispositionedimmediatelybelowthisweight,beneaththeplastic,atthelowestpointofthepit,andatuberunsfromtheburiedcupbackuptothegroundsurfacesothatwatercanberemovedafterwards.Thewayitworksisthatimpurewaterinthehumidsoiloutsidetheburiedcupisevaporatedbysunlightshiningthroughclearplastic.Thepurewatervapou
8、rcondensesonthecoolinsideplasticsurfaceanddripsdownfromtheweightedlowpoint,whereitcollectsintheburiedcupandisthenremovedusingthetube.Thebasicprinciplesofsolarwaterdistillationaresimpleyeteffective,asdistillationreplicatesthewaynaturemakesrain.Thesunsenergyheatswatertothepointofevaporation.Asthewater
9、evaporates,watervaporrises,condensingontheplasticsurfaceforcollection.Thisprocessremovesimpuritiessuchassaltsandheavymetalsaswellaseliminatingmicrobiologicalorganisms.Theendresultiswatercleanerthanthepurestrainwater.Solarstillsareusedincaseswhererain,piped,orwellwaterisimpractical,suchasinremotehome
10、sorduringpoweroutages.InFloridaandotherhurricanetargetareasthatfrequentlylosepowerforafewdays,solardistillationcanprovideanalternatesourceofcleanwater.Solarstillsareoccasionallyusedonalongertermbasisindevelopingworldsettings.However;dependingonenvironmentalconditions,theyusuallyproducearelativelysma
11、llamountofwater;andevenlesswherethesourceissalineorbrackish.Ifthesourceisinadequate,acompromisemethodistomixthedistilledwaterwiththebrackishorsalinewaterpurifiedwithothermethodsasthisgivesamoreadequatequantityandre-introducestheothersourcecontaminants,whilestillloweringthesalinity,andimprovingthetas
12、te.Knowinghowtoputtogetherasolarstillcanprovetobeausefulsurvivalskillandcouldprovideanimportantmeansofobtainingpotablewaterintheeventofawildernessemergency.Nevertheless,undertypicalconditionsmakeshiftsolarstillsrarelyproduceenoughwaterforlong-termsurvival,andthesweatexpendedinbuildingonecaneasilyexc
13、eeditsdailyoutput.Solarstillscanextractwaterfrommoistureinthegroundbuttoincreasetheamountofmoistureavailabletoasolarstill,water(freshorsaline)canbeaddedinsideoralongtheedgesofthestill.Wherenowatersourcesarereadilyavailable,shreddedvegetation,wetsoilorsand,orurineorcoveredfaeces,canbeusedinsidethepit
14、.Ifonlythenaturalsoilmoistureisused,thepitmusteventuallybemovedastheproductivitydrops.Adaptedfrom:https:en.WikiboOkS.orqWiki/DrinkinqWater/Disinfection/SOIarandhttps:en.WikiboOkS.orqWiki/DrinkinqWClter/DistillationQuestions1-4ChoosetheappropriatelettersA,B,CorD.Writeyouranswersinboxes1-4onyouranswer
15、sheet.1. SODISA. isseldomusedinthedevelopingworld.B. istypicallymadeuseofindomesticsettings.C. isusedtomeltandrecycleplasticPETbottles.D. canbeexpensive.2. ThePETbottlesusedinSODISA. mustbefilledtothetopbeforetheprocessbegins.B. shouldhaveatleasta2-litrecapacity.C. shouldbepositionedonaslantingmetal
16、surfacetogetthebestresults.D. musthaveahighturbidityindex.3. AsolarstillA. makesuseofthesameprocessthatisusedtoproduceraininnature.B. requirestheuseofsalttopurifymetals.C. involvesthecollectionofimpurerainwaterinaburiedcup.D. isawayofmeltingandrecyclingclearplastic.4. SolarstillsA. areoftenusedincombinationwithwells.B. canbeimpracticalinhurricanes.C. donotprovidemuchwaterinsalineconditions.D. areuncommoninFlorida.Questions5-9
