WATERSANITATIONFORPLANTPRODUCTION
Essentiallyanysizenurserycaninstallawaterrecyclingandsanitationsystem.Thishandoutwillfocuson
sanitation.However,wewillbrieflydiscussallfivesteps,sincebetterwaterqualityimproveseffectivenessof
manysanitationtreatments.
Therearebasicallyfivestepsthatareperformedwhenrecyclingandtreatingwater:
1)Collectionofrunoffwater
2)Removaloffloatingdebris
3)Removalofsuspendedparticulatematter(sand,silt,clay,organicmatter)
4)Sanitation–treatmentforpathogencontamination
5)Controloffertilizerlevels
1.Collectionanddetentionofuntreatedandtreatedwatersupplies
a.Detentionbasinsize–Ifrunoffwaterisbeingcollected,thesizeofthecollectionbasinmustbeconsidered.In
addition,abasinforsanitizedwatershouldbeconsidered,thesizeofwhichwillbedeterminedbythewater
demandsofthenursery.
b.Locationofcollectionbasin(s).Thetopographyofthenurseryandspaceavailablemustbetakeninto
consideration.Also,iftherearedifferenttypesofproductionsites,i.e.propagation,plugproduction,field
crops,orcontainercrops,theremaybemultiplewatersourcesandwaterrecyclingunits.Ifthenurseryis
situatedonahill,thenthecollectionbasincanoftenbelocatedatthelowerelevationsothatgravitycanbe
usedtocollectrunoff.
2.Removaloffloatingdebris
Mostfloatingdebriscaneasilyberemovedviabaffleslocatedatornearthecollectionbasinorsedimentationpits.
3.Removalofsuspendedmaterial
Severaltypesofmethodsmaybeimplementedtoremovesuspendedmatterfromrunoffwater.Thetechniqueto
usewillbedeterminedbythedegreeofpurificationdesiredandthetypeofsuspendedresiduesinthewater.
a.Sedimentationthroughgravity.Thisisthemostcommonandeconomicalprocessusedbynurseries.Most
suspendedmaterialwillsettleoutinthesedimentationpondorcollectionbasinwithinafewhours.However,
clay,beingaveryfinecolloidalmaterial,mayrequireseveraldaystosettleoutofthewater.Sedimentationpits
willneedtobecleanedoutoccasionallytoremovethebuildupofparticulatematteronthebottom.
b.Flocculation.Thisistheprocesswhereacombinationofferricsulfate,alum,orapolymerareaddedtothe
watertoflocculatethesuspendedclayparticles,resultinginarapid(5minutes)sedimentationofflocculated
clay.
c.Sand/Charcoalfiltration.Thisprocessisdonetofilteroutanyremainingsuspendedmaterials.
4.Sanitation
Runoffwaterandirrigationwaterderivedfromsurfacewatersusuallycontainplantpathogenssuchas
Phytophthora,Pythium,etc.Severalmethodsofsanitationavailableonthemarket.Thetypeofmethodtousewill
bedeterminedbythecleanlinessofthewater,thedegreeofsanitationdesired,thetypeorrecyclingsystembeing
used,andlocalregulations.
5.Fertilizerinjection
Fertilizerinjectionisusuallythefinalstepintheprocess,sincevarioussanitationmethodsmaydenaturefertilizer
chelatessuspendedinthewater,orevenremovefertilizerfromthewater.Fertilizerblendingisusuallydonein
conjunctionwithmixingoffreshwaterwithrecycledwaterinawaythattheelectricalconductivitydoesnot
increaseintheproductionsystem.
AmericanHort provides this on a “Not For Publication” basis. Publication of this information, in part or
whole, is only permissible through written permission
of the author(s).
Page1of12
SANITATIONMETHODS
Thelistofthemostcommonsanitationmethodsareasfollows:
a.Chlorination
b.Slowsandfiltration
c.Rapidsandfiltration
d.Membrane‐mediatedfiltration
e.Heat
f.Ultravioletlight
g.Ozonation
h.Copperionization
Caution–
1. Testasanitationmethodbeforeinstallingonalargescale.Beforepurchasingandinstallingatreatment
system,asmallpilotsystemshouldbetestedtomakesurethetreatmentmethodworksforyournursery.
Newmethodsofwatersanitationareoccasionallydevelopedandmarketed,buttheymaynotbesuitablefor
youroperation.
2. Routinelycheckefficacyofsanitationsystem.Onceasanitationsystemisinstalled,itshouldberoutinely
inspectedandtestedtomakesurethateffectivesanitationprocessesareoccurring.
3. Keeprecords.Maintainalogofthesystemforeaseoftroubleshootingifproblemsdooccur.
4. RegulationsandSafety.Followallapplicableregulationsandsafetyprocedures.
CHLORINATION
Chlorinetreatmentisoneofthemostpopularmethodsutilizedforthecontrolofhumanandplantpathogens.
Whenchlorineisaddedtothewatersupply,asidefromkillingpathogens,itmayalsobindtoorganicmatteror
chemicalssuchammoniacalnitrogen.Ifchlorinebindstoorganicorchemicalcomponents,thechlorineis
consideredunavailableforpathogencontrol.Thereforetheeffectiveor‘residual’chlorineconcentrationis
reduced.Thisisthereasonthatchlorinationismoreeffectivewithwatersourcesthatarenotheavily
contaminatedwithorganicmatter.Whenmostpathogensareexposedtohighenoughconcentrationsofchlorine
forasufficientperiodoftime,theywillbekilled.
Effectivenessoftreatmentisinfluencedbysixfactors:
(1)Chlorineconcentration–Thegreatertheconcentration,themorequicklyitdisinfects.However,toomuch
chlorinemayalsokillplants.Mostplantsaresafeifresidualchlorineconcentrationsare<100ppm(3
meq/L),andirrigationisappliedtotherootmedia.However,somecropsareverysensitivetochlorine.
Also,someplantswillbesensitivetochlorineirrigationwaterappliedtoleavesatmuchlower
concentrations,whichcancauseleafspots.
(2)Durationofpathogenexposuretochlorine–Effectiveexposuretimesmayrangefrom1minuteto24hours.
(3)Initialcleanlinessofwater–Dirtywatertiesupchlorine,reducingdisinfectantefficacy.
(4)WaterpH–Chlorineismorestable,andthereforemoreeffective,whenirrigationwatershaveaneutralpH.
(5)Pathogentype.Somepathogenswhichhavethecapabilityofformingdormantcystsorweedseednodules,
whichcanallowthemtosurvivetreatmentwithchlorine
(6)Watertemperature–Relativelyhigh(>20C)orlowtemps(<10C)maydecreasetheeffectivenessofchlorine.
Advantages
+Operationcosts–Sincechlorineinjectionrequireslimitedenergy.
+Capitalcosts–Low.Mostcostsareforchlorine.
+Exposuretime–Mostpathogensarekilledwithinsecondstoafewminutesofchlorineexposure.
+Technicalcomponents–Fewtechnicalcomponentsifsodiumorcalciumhypochloriteisused.
Page2of12
+Maintenance–Lowmaintenancerequirements.Ifchlorinegasisused,theinjectionsystemwillneedtobe
inspectedperiodically.
+Adaptability–Veryadaptabletosmallandverylargeproductionsystems.
+Chemicalcontrol–Properlyperformedchlorinationshouldnotaffectthechemicalnatureofthewater.
+Space–Asidefromchlorinestorage,noadditionalspaceisrequired.
+Labor–Systemislow‐laborinput.Manualadditionsofliquidchlorinecanbedone.Somelaborisrequiredto
routinelycheckequipmentifchlorinegasisused.
Disadvantages
–Chemicals–Athighconcentrations,residualchlorinecankillplants.Atlowerconcentrations,residualchlorine
cancauseleafspotswhenwaterisappliedtoleaves.Someplantsaremoresensitivethanothers.Organic
matterinwaterandmediausuallytiesupexcesschlorinebeforesignificantdamagecanoccuroncrops,except
forinhydroponicsystemsorwithsensitiveplantspecies.
–Safetyandregulation–Allformsofchlorinehavetherequirecautionwithworkersafety.Chlorinegasin
particularrequiresadditionalsafetytrainingandprecautions,anditsuseandstoragemayberegulatedby
governmentagenciesorcompaniessellingtheproduct.Otherformsofchlorinearehazardousintheir
concentratedforms.
–Herbicideandpesticideremoval–Chlorinedoesnotbreakdownorremovemostpesticidesorherbicides.
–Floatingdebrisremoval–Largersuspendeddebrisshouldberemoved,sothatfreechlorineisnotinactivated
byorganicmatter.
–Dissolvedorganicmatter–Colorationduetodissolvedorganicmatterandacidsisnoteliminated.
ChlorinationMethods.Thereareseveralformsofchlorineavailablefordisinfections,eachwithmethodsof
incorporatingchlorineintoirrigationwater:
(1)ChlorineGas–Thisisprobablythemostcommonandtheleastexpensivefornurseryandgreenhouse
sanitation.However,chlorinegasisdangeroustoworkwithandtherearemanyregulationsthatdictateits
storageanduse.Ifchlorinegasisconsidered,checkwithlocalagenciesforthenecessarypermits.
(2)Sodiumhypochlorite–Commercialbleachwhichhas100,000–140,000mgchlorine/L.Thisisoftenusedin
theindustry.
(3)Calciumhypochlorite–Whichhas350,000mgchlorine/L.Thisisoccasionallyused,especiallyifsodium
buildupisaconcernwiththeuseofsodiumhypochlorite.Italsocomesintabletform,whichmaybemore
convenientandsafertohandle.
(4)Onsitegeneration–Hypochlorousacidandchlorinedioxidecanbegeneratedonsitewithspecialized
equipment.Whiletheinitialcapitalcostsmaybehigherthatothermethodsofchlorine,onsitegeneration
hastheadvantageofeliminatingtheneedforstorageofchlorineproducts,thusreducingsafetyconcerns.
Note:ChlorineasadisinfectantforwaterhasbeenbannedrecentlyinsomeEuropeancountriesduetothefact
thatchlorinewillreactwithhumiccompoundstoformtrihalomethanes,whicharetoxictohumanhealth.
SLOWSANDFILTRATION(SSF)
Slowsandfiltration(SSF)isamethodoffilteringwaterthroughfinesand(0.15–0.35mm).Unlikecoarsesand
(1.0–2.0mm),finersandstrapsomepathogensandalsoallowbeneficialmicroorganismstodeveloponthesand
surface,whichkillpathogenicbacteria,fungiandcertainviruses.Efficiencyisbasedon1)sandparticlesizeand2)
thebeneficialmicroorganismsthatdeveloponthesandsurface(‘Schmutzdecke’),whichactivelybreakdown
pathogensviachemical,physical,andbiologicalmeans.
Effectivenessoftreatment.Physically,pathogenscanbetrappedinthefinesandofthefilter.The
biological/chemicaleffectisthroughthebeneficialorganismsthatdeveloponthesurfaceofthesand.Thisliving
matrixhasbeenshowntoeliminatepathogenssuchasPhytophthora,Pythium,Cylindrocladium,Fusarium,
Verticilliumdahliae,Thielaviopsis,andXanthomonas.Forexample,inonestudywithgreenhouse‐growntomatoes
Page3of12
growinginrockwool,thecontrolofPhytophthoracinnamomiinrecycledwaterwas100%,whenfine(0.15–0.35
mm)andmedium(0.20–0.80)gradesands,ratherthancoarsesands(0.5–1.60mm)wereusedandtheflowrates
werelow(10cm/hcomparedto30cm/h).Basedonthisandotherstudies,flowratesof100to300
liter/hour/meter2arerecommended.Theslowertheflowrates,themoreeffectivethesystemisintrappingand
killingpathogens.
Advantages
+Operationcosts–Lowenergycostssincethesystemworksthroughgravity.
+Installationcosts–Low.Financialoutputsareprimarilyforretentionbasins.
+Chemicals–nochemicalsrequiredtokillpathogens(mostorganisms.)
+Technicalcomponents–Notechnicalcomponentsorcontrolsystems.
+Maintenance–Lowmaintenancerequirements.
+Adaptability–Adaptabletowiderangeofproductionsystems.
+Pathogenremoval–AnestablishedSSF,whereabiologicalactivefilmhasformedontopofthesand,will
removeand/orbreakdownpathogens.
+Chemicalcontrol–ProperlymaintainedSSFsdonotalterthepHoftheeffluentwater.
Disadvantages
–FiltrationTime–Longerfiltrationtime(0.05–0.55gpm/ft2)thanrapidsandfiltration(2.0–20gpm/ft2).
–Labor–Occasionalcleaningmaintenancerequireslabor.
–Space–Requiresapproximatelyfourtimesmoresurfaceareathanrapidsandfiltration.
–Herbicideandpesticideremoval–Abilitytofilterorbreakdownherbicidesandpesticidesdoesnotoccur,but
placementofalayerofgranular‐activatedcarbon(charcoal)canadsorbcertainorganicherbicidesand
pesticides.
–Floatingdebrisremoval–Largersuspendeddebrisshouldberemoved,sothatintervalsbetweencleaning
filtersisextended.
–Dissolvedorganicmatter–Colorationduetodissolvedorganicmatterandacidsisnotalwaysremovedthrough
SSF.
StructureandOperationalConsiderations
Housing.Thesandfiltercanbehousedinacementtanks,plastic,orfiberglassdrumsorcontainers.Itis
recommendedtohavetwosmallerunitsratherthanonelargeunit,sothatonesystemcanbeshutoffforcleaning,
whilestillhavingtheotherunitoperating.
Filtrationcomponents.
*Inletstructure–Theinletforuntreatedrunoffwatershouldbeconstructedsothatthesandsurfaceisnot
disturbedbyincomingwater.
*Water–Aconstantdepthofapproximately1meterofsupernatantwatershouldbeontop,theweightofwhich
allowspercolationthroughthesandbelow.
–Stability.Thewaterlevelshouldnotfluctuate,sothatflowratesthroughthesandcolumndonotchange.
Variableflowratesdecreasefilteringperformance.
–Level.Thewaterlevelshouldnevergobelowthelevelofthesandfilter.Thewatercolumnprotectsthe
beneficialbiologicallyactivefilm/filterthatdevelopsonthesandsurface.Hightemperaturesanddrying
willkillorimpedetheactivityofthebiologicalfilter.
–Flowrates.Theflowrateshouldbecontinuous.Biologicalfilterswilldiethroughoxygenstarvationin
stagnantwater.
*Organicfilm–Thisorganicfilm,called‘Schmutzdecke’,isalayerofbeneficialmicroorganismsandorganic
matterthatnaturallydevelopontopofthesandfilterbed.Thisisthekeycomponentthatfiltersand/orkills
manypathogens.
*Sand–Alayerofsand80–150cm(32–60inches)deep.
–Particlesize.Particlesizeof0.15to0.35mmisrecommended.
–Uniformitycoefficient.Theuniformitycoefficient(UC)ofthesandshouldbelessthan5,butrecommended
tobelessthan2.TheUC=d60/d10,whered60isthesievesize,inmm,thatallowspassagethroughthesieve
Page4of12
of60%ofthesand(byweight),andd10isthesievesize,inmm,thatallowspassagethroughthesieveof
10%ofthesand(byweight).
*Granularactivatedcharcoal–Optional.Thisadsorbsmostorganicchemicalssuchaspesticidesandherbicides.
Thiscanbeplacedinbetweenthesandcolumn.Placednewthesurface,theactivatedcharcoalshouldbe
replacedwhenthetoplayerofsandisreplaced.
*Gravelbed–Alayerofgravelpreventssandfromblockingthetreatedwateroutlet.Inmoresophisticated
systems,threedifferentgradedlayersofgravelareused:2–8mm,8–16mm,and16–32mm.
*Drainpipe–Aperforateddrainagepipeisplacedinthebottomlayerofgravel.Additionalfilteringcanbe
accomplishedwithatextilefabricplacedoveroraroundthedrainagepipe.
*Flowmeterandcontrolvalve–Foroptimalperformance,flowratesshouldbeconsistentlymaintainedwiththe
installationofacontrolvalveattheendofthedrainpipe.
Operationalsettings
*Filtrationrate–10–30cm/hr(2.5–7.5inches/hr).Lowflowrates(10cm/hr)arerecommendedwhencontrol
ofpathogenssuchasFusariumarerequired,whilehigherflowratesof30cm/hr)aresuitableforthecontrolof
pathogenssuchasPhytophthoraandPythium,whicharecommonlyfoundinnurseriesproducingcontainerized
woodyornamentals.
*Filtercapacity–100–300L/m2/hr(25–75gal/yd2/hr).
Maintenance–Whenflowratesdiminish,theupper1–4cmofsandareremovedalongwiththebiological
‘schmutzdecke’layerthatdevelopedonthesurface.Thefrequencyofthismaintenanceisbasedonthecleanliness
oftherunoffwater,watertemperature,andamountofwaterbeingfilteredinagiventimeperiod.Cleaning
frequencyintervalsmayrangefromeveryseveralweekstoeveryseveralmonths.
RAPIDSANDFILTRATION(RSF)
Intheliterature,RapidSandFiltration(RSF)isusuallyreferredtoas‘SandFiltration’.However,forclarityofthis
articleitwillbereferredtoasRapidSandFiltration(RSF)todifferentiateitfromSlowSandFiltration(SSF).RSF
utilizescoarsesand(>1.0mm)andpossiblyothersubstratessuchasactivatedcharcoal.Unlikethefinersands
utilizedinSSF,RSFdoesnottrapmanypathogens;therefore,additionalmeansofwatersanitationsuchas
chlorination,maybeneeded.
Advantages
+Operationcosts–Lowenergycostssincethesystemworksthroughgravity.
+Installationcosts–Low.Financialoutputsareprimarilyforretentionbasins.
+Filtrationtime–Filtrationprocessesarerapid(15–25gpm/ft2)comparedtofiltrationratesforSSF(0.05–0.55
gpm/ft2).
+Maintenance–Routinebackflushingrequiresminimalinput.
+Chemicalcontrol–ProperlymaintainedRSFdonotalterthepHoftheeffluentwater.
+Space–RequireslesssurfaceareathantraditionSSFsystems.
Disadvantages
–Chemicals–Otherchemicalssuchaschlorinemayberequiredtokillpathogens.
–Labor–Occasionalcleaningmaintenancerequireslabor.
–Herbicideandpesticideremoval–Doesnotfilterorbreakdownpesticideandherbicides,butplacementofa
layerofgranular‐activatedcarbon(charcoal)canadsorbcertainorganicherbicidesandpesticides.
–Floatingdebrisremoval–Largersuspendeddebrisshouldberemoved,sothatintervalsbetweencleaning
filtersisextended.
–Dissolvedorganicmatter–Colorationduetodissolvedorganicmatterandacidsisnotalwaysremoved.
Page5of12
StructureandOperationalConsiderations
Housing.Thesandfiltercanbehousedinacementtanks,orcompletelyenclosedsteeltanks.Itisrecommended
tohavetwosmallerunitsratherthanonelargeunit,sothatonesystemcanbeshutoffforbackwashing,utilizing
thewaterfromtheothersandfilter.
Filtrationcomponents.
*Inletstructure–Theinletforuntreatedrunoffwatershouldbeconstructedsothatthesandsurfaceisnot
disturbedbyincomingwater.
*Water–Aconstantdepthofapproximately1meterofsupernatantwatershouldbeontop,theweightofwhich
allowspercolationthroughthesandbelow.
–Stability.Thewaterlevelshouldnotfluctuate,sothatflowratesthroughthesandcolumndonotchange.
Variableflowratesdecreasefilteringperformance.
*Sand–Alayerofsand,thethicknessofwhichisvariable.
–Particlesize.Particlesizeof1mmandlargerisused.Asthecoarsenessofthesandincreases,thespeedof
filtrationwillincreasebutthequalityofthefilteredwaterwilldecrease.
–Uniformitycoefficient.Theuniformitycoefficient(UC),asdescribedinthesectiononSSFshouldbeno
morethan5,butnolessthan2.However,parametersofthisnaturehavenotbeendefinedforcoarse‐sand
filtersusedinRSF.
*Granularactivatedcharcoal–Optional.Thisadsorbsmostorganicchemicalssuchaspesticidesandherbicides.
Thiscanbeplacedinbetweenthesandcolumn.
*Gravelbed–Optional.Alayerofgravelpreventssandfromblockingthetreatedwateroutlet.Inmore
sophisticatedsystems,threedifferentgradedlayersofgravelareused.
*Drainpipe–Optional.Aperforateddrainagepipemaybeplacedinthebottomlayerofgravel.Additional
filteringcanbeaccomplishedwithatextilefabricplacedoveroraroundthedrainagepipe.
*Flowmeterandcontrolvalve–Foroptimalperformance,flowratesshouldbeconsistentlymaintainedwiththe
installationofacontrolvalveattheendofthedrainpipe.
Operationalsettings
*Filtrationrate–15–25gpm/ft2(900–1,500gph/ft2).UnlikeSSF,lowerflowratesdonotassistinthecontrolof
pathogenssincethesandissocoarse.
*Filtercapacity–Filtercapacitywilldependonthetypeofsystembeinguse.However,thefiltrationrateof
900–1,500gph/ft2,makesthissystemsuitableforthelargescalenurseries(>100acresthatareusing
overheadirrigation.
Maintenance–Frequencyofmaintenanceisdictatedbythedirtinessofthewater.Dailybackwashingisnot
uncommon.Thedebrisfromthebackwashmaybepumpedbackintothereservoir,pumpedintofields,ordrained
andcomposted.However,oneshouldcheckwithlocalagenciesregardingregulationspertainingtothedisposalof
backwashdebris.
MEMBRANE‐MEDIATEDFILTRATION
Therearebasicallyfourtypesofmembrane‐mediatedfiltrationprocesses:(1)ReverseOsmosis,(2)Nanofiltration,
(3)Ultrafiltration,and(4)Microfiltration.Allofthesetechniquesinvolvepassingwaterthroughmembranes,
whichfilteroutunwantedsubstances.Pressure(energy)isrequiredtopumpthewaterthroughthemembranes,
withthesmaller‐poredmembranesrequiringmorepressuretoforcewaterthroughtheporescomparedtothe
largerporedmembranes.Themajordifferencesbetweenthesesystemsarethesizesofthemembranepores.The
advantagesanddisadvantagesofthesesystemsaredescribedinTable1andtherelativesizesandweightsof
chemicalsandorganismsfoundinirrigationwateraredescribedinTable2.
ReverseOsmosis(RO)–Alsocalledhyperfiltration,utilizesmembraneswiththesmallestporesofthefourfilter
systems.Becauseofthesmallpores,ROremovesdissolvedsalts,chargeparticles,andcompoundsofmolecular
Page6of12
weightgreaterthanabout200daltons(1dalton=1atomicmassunit[amu]),aswellasmostpathogens.Nurseries
thatareforcedtouselowquality(salty)water,usuallymustutilizeROtoremovedissolvedsalts.Sincethis
processremovesdissolvedsalts,includingfertilizer,donotutilizethismethodafterfertilizerhasbeenaddedto
theirrigationsystem;otherwisethefertilizerwillberemovedfromthewater.
Nanofiltration–UtilizesmembranesofalargerporesizethanthoseusedinRO;however,poresarestillsmall
enoughtofilteroutlargersizedmolecules(≈200–1000daltons).Theseporesareusuallylargeenoughtoallow
chelatednutrientstopassthrough,sincemostchelatessuchasiron‐EDTAhaveamolecularweightunder500
daltons.Also,somechargedparticlesmaynotpassthroughthesefilters.
Ultrafiltration–Utilizesmembraneswithporesizesofapproximately1.0to20nm,whicharelargerthanporesof
nanofiltrationsystems.Nodissolvedsalts(fertilizer)willberemovedwiththissystem.However,ultrafiltration
willstillremovesuspendedclayandpathogenssuchasbacteria,nematodesandmostfungalsporesandsome
viruses.However,somesmallerviruseswillnotberemoved.Therefore,itmaybenecessarytodoaddition
sanitationtreatmentstothewater.
Microfiltration–Utilizesmembraneswithporesizesofapproximately100to10,000nm(0.0001to0.0100mm).
Whilethisfiltrationsystemrequirestheleastamountofenergytopasswaterthroughthemembranes,italsodoes
notscreenoutmostpathogens;therefore,additionalsanitationtreatmentswillberequired.Thisprocessis
sometimesusedbeforetheROprocess.
Table1.Physicalcharacteristics,costofoperation,andadvantagesanddisadvantagesoffourtypesofmembrane‐
mediatedfiltrationsystems.OneDalton=1atomicmassunit(amu)
Membrane
type
Reverse
Osmosis
Approximate
Relative
filtrationporesize cost
0.1nm
High
Nanofiltration
1.0nm
Moderate
Ultrafiltration
1to20nm
Low
Microfiltration
100to10,000nm
Lowest
Advantages
Disadvantages
* removeschargedions (incl.salts)
*removescompounds≥250amu
*almostessentiallyallpathogens
* removessomechargedions.
*removescompounds≥200–1000
amu
*removesessentiallyallpathogens
* removesbacteria
*fungalspores
*removesnematodes
* requiresleastamountofenergy
*removesdissolvedfertilizer
*mayremovesomechelates
*virusmaynotberemoved
*manypathogenswillnotbe
removed
Table2.Relativesizesofwaterandfertilizermoleculesandsomecommonpathogenssometimesfoundin
irrigationwater.Sizesofpathogensareranges,sincetherearemanytypesofviruses,bacterialandfungi.Please
notethatthereisnocorrelationbetweenweightandsize,sincesomeorganismmaybedenser(heavier)thanother
organismsorchemicalsofthesamesize.
Organism/particle
Watermolecule
Iron‐EDTAchelate
virus
E.coli
Fungalspores
nematodes
Weight(Daltons) z
18
526
7,000,000
Over3,000,000,000
NA
NA
Size(nm)
0.20nm
NA
20to200nm
2000nm
2000to5,000nm
300,000nmandlarger
zAdaltonisequalto1atomicmassunit(amu).
Maintenance
*Flushing–Allmembranesystemswillrequireperiodicflushingofmembranes,thefrequencyofwhichis
dependentonthecleanlinessandthevolumeofwaterbeingtreatedduringagiventimeperiod.
Page7of12
*ConcentrateDisposal–Theresiduescollectedwillneedtobedisposedof,themethodofwhichwilldependon
regulationsinyourregion.
*Membranereplacement–Membraneswillneedtobereplacedafteragivenperiodofusage.
HEATDISINFECTION
Usingheattosanitizematerialshasbeencommonlyusedtosterilizerootmediainthenurseryindustry.Heathas
alsobeenusedtosterilizewater,especiallyfornurseriesinEuropeancountries.Sincenochemicalsareaddedin
thisprocess,thereisnoconcernregardingchemicalstorageorchemicalresidues.
Howdoesheattreatmentwork?
Alllivingorganismshaveacertainheattolerance,theabilitytowithstandacertainmaximumtemperaturefora
specifiedperiodoftime.Oncethistimeortemperatureisexceeded,theorganismdies.Virusesarekilledat
temperaturesaslowas130F(55C)ifthattemperatureismaintainedforaperiodof1.5hours.Athigher
temperatures,therequiredheatdurationfororganismdeathdecreases.
Proceduresforheattreatment
Metalheatexchangersaresituatedatonepointalongthewatertreatmentsystem.Thenumberandsizeof
exchangerswilldependonthevolumeofwaterthatneedstobetreatedduringagiventimeperiod.Priorto
passingovertheheatexchanges,thewaterpHmaybeacidifiedto4.5topreventcalciumaccumulationonthe
exchangers.Ifthewaterisparticularlydirty,filtrationmayberecommendedpriortoheattreatment.After
heating,thewatermustbecooledbeforeusingonplants.
Advantages
+Nochemicalresidues–Sincenochemicalsused.
+Noadditionalchemicals–Properheatingprocedureswillrequirenochemicaltreatment.
+Maintenance–Nomaintenance,unlesscalciumbuildsuponexchangers.
+Pathogencontrol–Allpathogenswillbekilled.
+Algaecontrol–Thesystemwillkillalgae.
+Plantsafe–Ifcooledsufficientlyafterheattreatment,therearenopotentialtoxicitiesfromheating.
Disadvantages
–Difficultmonitoring–Watermustbecheckthroughlaboratoryprocedurestoensurethatthatallpathogensare
killed.
–Watercooling–Watermustbecooledpriortousage.
–Lengthytreatmentperiod–Dependingonthemaximumtemperatureutilized,heatingdurationmaytakeupto
1.5hourstoachieve100%mortalityofpathogens.
–Spaceallocation–Sincetheefficacyofheattreatmentisrelatedtoexposuretimeatacertaintemperature,
tankswillbeneededtoholdtreatmentwaterandcoolingwater.
–Highoperationcost–Forelectricalsource,naturalgas,oroil.
–WaterpH–WaterwillrequireacidificationtoapHofapproximately4.0–4.5priortoheating(toprevent
calciumbuilduponheatexchangers),andthenwillhavetobeneutralized(tocroprequirements)afterheat
treatment.
–Floatingdebrisremoval–Doesnotbreakdownorremovefloatingdebris.
–Clayandsiltremoval–Claysandothersoilparticlesarenotremovedorbrokendown.
–Chelatesdestroyed–Ifchelatesforironorothernutrientsareused,temperaturesupto150Fshouldnotbea
problem.However,accidentaltemperaturesnearboiling(212F)willdenaturechelates.
–Pesticidebreakdown–Pleasecheckpesticidelabelsfortemperaturestabilitiesinsolutions.
Page8of12
ULTRAVIOLETLIGHT
WhatisUltravioletlightandhowdoesitwork.
Ultravioletlightfitsintothelightspectrumofwavelengthsfrom100‐400nanometers(nm).Thisisthesamelight
wavelengththatisnotoriouslyknowntocauseskincancerinhumans.Visiblewavelengthsrangefrom390‐810
nm.TheUVlight,likechlorinetreatments,killsthepathogens(bacteria,fungi,andviruses)suspendedinwater.
However,sinceitisalightsource,thewatermustbecleanofsuspendedclaysandorganicacids.
Ultra‐violetlightsources.
TherearethreetypesofUVsources:(1)lowpressuremercuryvaporlamps;(2)Xenonflashlamps;and(3)excimer
lasers.Low‐pressuremercurylampsemitawavelengthof254nm.Theuseof‘high’pressuremercurylampsmay
alsobeused,buttheyalsoemitwavelengthsof190nm,whichresultsintheformationofozonewhichcanalso
sanitizethewater.Xenonflashlampsemitpulsesoflightthatisahigherpowersourceofemission.However,
Xenonlampsalsoemitwavelengthsoveralargerspectrum,someofwhicharenotUV,makingXenonlampsless
energyefficient.ThethirdsourceofUVlightistheexcimerlaser,whichemitspulsesoflight(248nm).
*Advantages
+Operationcosts–Costofoperationwillbelowifthewatersourceisclarified.
+Installationcosts–Relativelylowerforcleanerwatersupplies.
+Chemicals–Nochemicals,regardlessofthelightsourceutilized.
+Technicalcomponents‐‐Fewtechnicalcomponentsorcontrolsystems.
+Pathogenextermination–Killsbacteriaandfungiandviruses.
+Chemicaleffects–NoeffectonwaterpH.
+Space–Smallspacerequiredforinstallationoflightsourceandpowersupply.
+Algaecontrol‐‐Thesystemwillkillalgaesuspendedinthewatersource.
+Nontoxictoplants–UVtreatedwaterhasnotoxiceffectonplants.
*Disadvantages
‐Chemicaleffects–lightsourceswillchemicallydenaturechelates.
‐Effectiveness–OrganicacidsorclaywillreduceefficacyoftheUVlighttreatment.
‐HerbicideandPesticideremoval‐‐Doesnotremoveotherchemicalsfromthewater.TheeffectsofUVlightmay
breakdownlight‐sensitiveherbicidesandpesticides.Consultmanufacturerforspecificchemical
questions.
‐Floatingdebrisremoval‐‐Doesnotbreakdownorremovefloatingdebris.
‐Dissolvedorganicmatter‐‐Colorationnotremoved.
‐Clayandsiltremoval‐‐Claysandothersoilparticlesarenotremoved.
‐Exposuretime–UVlightmayrequireanexposuretimeof30secondsorlonger,dependingontheclarityofthe
water.Slowerflowrateswillberequired,butlowerflowrateswillalsoreducewaterturbulenceand
efficiency.
OZONATION
Ozonekillspathogensthroughthechemicalprocessofoxidation.Ozoneisachemicallyunstablegasmoleculethat
consistsofthreeoxygenatomslinkedtogether.Thismoleculewouldliketohavetwomoreelectronstobecome
morestable,andthereforecan'take'electronsfromanothermolecule,oxidizingthatmolecule.Itis,therefore,
consideredanoxidant.Infact,ozone’soxidizingabilityistwicethatofchlorine.
Definitionsregardingoxidationandreductionprocesses
*Oxidant=anychemicalthatiscapableoftakingelectronsawayfromanotherchemical.Thesetypesof
chemicalreactionswereoriginallytermed'oxidation'becauseitwasbelievedthatoxygenwastheonly
chemicalabletotakeelectronsfromanothermolecule.Chemicalsotherthanoxygenarenowknowntobe
oxidants,buttheterm'oxidation'isstillused.Theabilityofaspecificchemicalenvironmenttocauseoxidation
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ismeasuredas'redoxpotential'(REDOX)or'oxidationreductionpotential'(ORP).ORPvaluesof700mv
shouldprovidecompletedisinfection.OPRvalueslessthan300mvareusuallyconsideredsafeformost
aquaticlife.
*Freeradical=anyatomormoleculethathasatleastoneunpairedelectron,buthasanoverall0charge.(Itisa
particlethatisneitherpositivelynornegativelycharged).Eventhoughafreeradicalhasachargeof0,ithas
theabilitytotakeelectronsfromothermolecules.Ozoneitselfisnotafreeradical,butwhenozonebreaks
down,oxygenfreeradicals(O·)andhydroxylfreeradicals(HO·)canbeproduced.
*Antioxidant=anychemicalthatprotectsanorganismfrombeingoxidizedoranychemicalthatinhibitsthe
abilityofoxidantstooxidize.Blueberriesaregoodforyoubecausetheyhavealotofantioxidants!
Note:Intheworldofoxidationreactionsandfreeradicals,twogeneralassumptionsinchemistrymustbe
understood:(1)mostcompoundsarestableatanelectricalchargeof0,and(2)electronsareonlystableaspairs.
Howdoesozoneworkindisinfectingirrigationwater?
Ozone,likechlorine,disinfectswaterbyoxidizingcellmembranesanddisruptingkeyphysiologicalreactionsin
livingorganismsandoxidizingdifferenttypesofchemicalssuspendedordissolvedinthewater.Inaddition,as
ozonebreaksdown,itproducesfreeradicals(Equation1).Thesefreeradicalsalsodisruptcellmembranesand
physiologicalprocessesbyupsettingtheelectronbalanceofthecellwallstructuresandchemicalpathways.
Equation1O3+H2OO2+2OH·
Ozone+wateroxygen+2freeradicalhydroxyls
Proceduresforozonationofirrigationwater
(1)Providearelativelypureoxygensource.Theuseofregularairwillnotworksinceitisonly21%oxygen.
(2)Electricallychargetheoxygen(O2),whichformsozone(O3).Thisisoftenperformedthroughcorona
dischargeorplasmadischargeunits.Over80%oftheenergyiswastedintheformofheat,whichmustbe
removedfromtheozonegenerator,sinceheatwilldecomposeozone.
(3)Bubbletheozonethroughthewatersource.Aninjectionrateof1oz.per1,000gallonsofwaterwithaone
hourexposuretimeistargetrate,butmayvaryaccordingtodifferentwatersources.Treatedwatershould
bemaintainedinaclosedpressurizedsystemtopreventoff‐gassingoftheozone.
(4)Ultravioletlightcanbeusedtoincreasetherateofbreakdownofozone,whichcausestherapidincreasein
freeradicalhydroxyl(·OH)groups.Thisactsasabetterdisinfectant.Thistechniqueiscalled'Advanced
PhotoOxidation'.
(5)Deactivateexcessozonebyventingthroughanactivatedcharcoalfilter.
Advantages
+Powerfuldisinfectantwithnochemicalresidues–Ozonebreaksdowntooxygen.Sotherearenochemical
residuesdirectlyfromozone.
+Noadditionalchemicals–Properozonationwillrequirenootherchemicalcontrol.
+Nochemicalstorage–Sinceozoneismadeon‐site
+Easymonitoring–EfficacyofsystemeasilymonitoredbymeasuringtheORP(redoxpotential).
+Maintenance–Lowmaintenanceunlessoxygensourceisnotclean,thenelectrodesmustbecleaned.
+Pathogencontrol–Mostpathogenswillbekilled.
+Algaecontrol–Thesystemwillkillalgae.
+Pesticidebreakdown–Manypesticideswillbeoxidized.
Disadvantages
–Lengthytreatmentperiod–Dependingontheamountoforganicmatterinwater,ozoneexposuremayrequire
upto20minutesto1hourtoachieve100%mortalityofpathogens.
–Spaceallocation–Sincetheefficacyofozoneisrelatedtoitsconcentrationandexposuretime,collectiontanks
fortreatedozonewaterwillbeneededsothatozonatedwatercanbestoredlongenoughforeffective
disinfection.
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–Highoperationcost–Forelectricalsource.
–IncreasedwaterpH–OzonewillincreasewaterpH,sowateracidificationmaybenecessary.
–Effectivenessreducedwithdirtywater–Organicmatterwillreactwithozone,decreasingtheamountofozone
availabletokillpathogens.
–Floatingdebrisremoval–Doesnotbreakdownorremovefloatingdebris.
–Pathogenresistance–Thechlamydosporesandmicrosclerotiaofsomepathogensaremoredifficulttokillwith
ozone.
–Clayandsiltremoval–Claysandothersoilparticlesarenotremovedorbrokendown.
–Chelatesdestroyed–Ifchelatesforironorothernutrientsareused,ozonationmayreactwiththechelates,
precipitatingthenutrientoutofsolution.
–Elementprecipitation–Ozonemayoxidizeandprecipitateoutofsolutionsomeessentialnutrientssuchas
iron,evenifchelatesarenotbeingused.
–Planttoxicity–Ozoneistoxictoplants,soozonelevelsshouldbebelowtoxicitylevelsbeforeapplyingtowater.
COPPERIONIZATION
Theuseofcopperandsilverionizationarepopularmethodsoftreatingdrinkingwaterforpathogens.Historically,
thesemethodsofwatertreatmentgainedpopularityaftertheoutbreakofLequionellapneumophila,thebacteria
responsibleforLegionnaires’disease,whichoccurredatthe58thstateconventionoftheAmericanLegionin
Philadelphia,Pennsylvaniain1976.Theconcentrationnecessaryforpathogencontrolisapproximately100ppb
fordrinkingwaterand20ppbtotreatpoolwater.
Howdoescopperionizationwork?
Ionizationworksviainsertingcopper‐coatedceramicelectrodesintoonepointofthewatersystem.Anelectric
currentpassesthroughthiselectrode,releasingcopperions(Cu2+).Thesepositively‐chargedcopperionsare
attractedtonegatively‐chargedparticles,suchasorganicmatter,siltandclayparticlesandtothemembranesof
bacteria,algaeandmold.Ifcopperbindstotheorganicmatter,siltorclay,thenthecopperbecomeschemically
inactive.However,ifthecopperbindstothemembranesoftheorganisms,theorganismsdie.
Copperinagriculture
Copperisaheavymetalthathasbeentraditionallyusedinagricultureasabactericideoncropsthrough
applicationsofcoppersulfate,whichhasbeenusedaloneorwithotherpesticides.Thoughitistoxictoplantsat
highconcentrations,copperisanessentialplantnutrient,andisrequiredatrelativelylowconcentrations(0.002–
0.003%)(20–30ppmplantdryweight).Inmostnutrientformulations,especiallymicronutrientblends,copperis
mixedintomediaatarateofapproximately0.01–0.40g/pot.Forhydroponically‐growncrops,copperissupplied
atconcentrationsofapproximately0.05ppm.Becauseofsuchrelativelylowrequirements,anyadditionalcopper
thatisaddedtoaplantsystem,eitherasapesticideorfertilizer,shouldbemonitoredsothatcoppertoxicityis
avoided.
Copperionizationinnurseryproduction
Copperionizationhasbeenusedsuccessfullyinagriculturalprocessessuchas:(1)coolantpadwatertreatmentto
keepfiltersfreeofalgaeand(2)postharvestwashingoffruitsandvegetables.Informationregardingcopper
ionizationusageinirrigationwaterrecyclingsystemsislimited.Inmostcopperionizationsystems,
recommendationsaretomaintainactivecopperionconcentrationsat0.50to1.5ppm.Copperelectrodesare
insertedintothewatersystem—preferablyafterthewaterhasbeenfilteredofdebrisandsuspendedclayand
organicmatter.Thenumberofcopperelectrodesrequiredwilldependontheamountofwaterthatneedstobe
treated,thecleanlinessofthewater(presenceoforganicmatterandsuspendedclay)andthesizeoftheelectrodes.
Someofthemodelscurrentlyavailablewilltreatabout200gallonsofwaterperminute.Additionalelectrodeswill
berequiredforhigherflowrates.
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Advantages
+Operationcosts–Moderate.Electrodereplacement(upto$10,000)andthecostofelectricity.
+Installationcosts–Low.Financialoutputsareprimarilyforinstallationofcoppercoatedelectrodesand
electricalsource.
+Chemicals–Somecompaniesclaimthatnoadditionalchemicalsarerequiredforpathogencontrol.However,
othersindicatethatoxidizerssuchaschlorinewillstillbeneeded,butatlowerconcentrations.
+Technicalcomponents–Fewtechnicalcomponentsorcontrolsystems.
+Maintenance–Low(occasionalreplacementofcopperelectrodes.)
+Pathogenremoval–Pathogenssuchasbacteriaandfungiwillbekilled.
+Chemicaleffects–CopperionizationwillnotalterthepHoftheeffluentwater.
+Space–Requiresnoadditionallandfortheconstructionoflargetreatmentfacilities.
+Algaecontrol–Thesystemwillkillalgaeonwaterandoncoolantpads.
Disadvantages
–Coppertoxicityofwater–Someornamentalcropsaresensitivetothecopperconcentrations(0.5–1.5ppm)
thatarerecommendedtoeffectivelytreatwater.Nodataisavailableoncopperaccumulationwithlong‐term
usageofcopperionizationinaclosedrecyclingirrigationsystem.Coppertoxicitywasdocumentedfor
chrysanthemum(Dendranthema),miniaturerose(Rosa),andgeranium(Pelargonium)at0.32ppm,0.15and
0.50ppm,respectively.
–Effectivenessreducedwithdirtywater–Sincecopperionsarepositivelycharged,theywillbeattractedtoand
bindtonegativelychargedparticlesoforganicmatterandclay,makingthecopperionsinactive.Therefore,
greaterinjection(releaserates)ofcopperionsfromelectrodeswillbeneededtokeepthecopperionsat
concentrationseffectivetokillpathogens.
–HerbicideandPesticideremoval–Doesnotremoveotherchemicalsfromthewater.
–Floatingdebrisremoval–Doesnotbreakdownorremovefloatingdebris.
–Dissolvedorganicmatter–Colorationduetodissolvedorganicmatterandacidsisnotremovedfromthewater.
–Clayandsiltremoval–Claysandothersoilparticlesarenoteffectivelyremovedwithcopperionization.
–Copperaccumulationinclosedrecyclingsystems–Copperwillbindtoorganicmatterandclaythatsettlesout
inreservoirs.Therefore,ifthissludgeisrecycledbackintothemedia,copperconcentrationsinthesludge
couldbetoxictosomecrops.Testsshouldbeperformedtocheckcopperconcentrationsofthesludgeand
mediabeforeuseoncrops.
Coppertoxicitysymptoms
Leaves:Reddishbrownlesions,whichcoalesceinseverecases.
Roots:Stuntinganddeathofroottipsandanincreasedproductionoflateralroots.Underseveretoxicitytheentire
rootsystemwillsenesce.
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