The Vertical Farm

36 Pages·2017·4.52 MB·English

buildings
Review
The Vertical Farm: A Review of Developments and
Implications for the Vertical City
KheirAl-Kodmany
DepartmentofUrbanPlanningandPolicy,CollegeofUrbanPlanningandPublicAffairs,
UniversityofIllinoisatChicago,Chicago,IL60607,USA;[email protected]
Received:10January2018;Accepted:1February2018;Published:5February2018
Abstract: Thispaperdiscussestheemergingneedforverticalfarmsbyexaminingissuesrelatedto
foodsecurity,urbanpopulationgrowth,farmlandshortages,“foodmiles”,andassociatedgreenhouse
gas(GHG)emissions. Urbanplannersandagriculturalleadershavearguedthatcitieswillneedto
producefoodinternallytorespondtodemandbyincreasingpopulationandtoavoidparalyzing
congestion,harmfulpollution,andunaffordablefoodprices. Thepaperexaminesurbanagriculture
asasolutiontotheseproblemsbymergingfoodproductionandconsumptioninoneplace,withthe
verticalfarmbeingsuitableforurbanareaswhereavailablelandislimitedandexpensive. Luckily,
recent advances in greenhouse technologies such as hydroponics, aeroponics, and aquaponics
haveprovidedapromisingfuturetotheverticalfarmconcept. Thesehigh-techsystemsrepresent
aparadigmshiftinfarmingandfoodproductionandoffersuitableandefficientmethodsforcity
farmingbyminimizingmaintenanceandmaximizingyield. Uponreviewingthesetechnologiesand
examiningprojectprototypes,wefindthattheseeffortsmayplanttheseedsfortherealizationof
theverticalfarm. Thepaper,however,closesbyspeculatingabouttheconsequences,advantages,
anddisadvantagesoftheverticalfarm’simplementation. Economicfeasibility,codes,regulations,
andalackofexpertiseremainmajorobstaclesinthepathtoimplementingtheverticalfarm.
Keywords: advancedcultivationmethods;innovativetechnologies;efficientfoodproduction;urban
populationincrease;sustainability
1. Introduction
1.1. Background
Thisresearchstemsfromalargerresearchprojectthatexaminedverticaldensityapplicationsto
the21stCenturyCity[1–3]. Ascitiestrytocopewithrapidpopulationgrowth—adding2.5billion
dwellers by 2050—and grapple with destructive sprawl, politicians, planners and architects have
becomeincreasinglyinterestedintheverticalcityparadigm. Unfortunately,citiesallovertheworld
aregrosslyunpreparedforembracingverticaldensity,becauseitmayaggravatemultidimensional
sustainabilitychallengesresultingina“verticalsprawl”thatcouldhaveworseconsequencesthan
“horizontal”sprawl. Onekeyproblemoffuturecitieswillbetransportinglargeamountoffoodto
servedensepopulation,andtheverticalfarmmodeloffersapotentialsolutiontothisproblem[1–5].
1.2. GoalsandScopeoftheStudy
As urban population continues to grow and as arable land is diminishing rapidly across the
globe, a fundamental change in food production is needed [4–7]. In particular, building-based
urban agriculture is increasingly needed in dense urban environments and a review of current
cultivationtechniquesandprojectswouldlikelytocontributepositivelytoacademicdiscussions[6–10].
Thisisparticularlyimportantsinceverticalfarmingengagesmultipledisciplinesofnaturalsciences,
Buildings 2018,8,24;doi:10.3390/buildings8020024 www.mdpi.com/journal/buildings
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architecture,andengineeringandaffectsbothpeopleandtheenvironment[9–11]. Thispaperattempts
toanswerthefollowingquestions:
• Whatisaverticalfarm?
• Whatarethedrivingforcesforbuildingit?
• Whataretheinvolvedhigh-techfarmingmethods?
• Whatarethesalientprojectexamplesonverticalfarming?
• Whataretheimplicationsfortheverticalcity?
1.3. Methods
Currently,wewitnessagrowingbodyofresearchonverticalfarming. Studiesandupdateson
thetopiccomeinmultipleformsincludingacademicpapers,professionalreports,newsarticles,blogs,
andwebsites,asdemonstratedinthispaperreferences. Thispaperpiecestogetherthesematerialsin
attempttoanswertheabovequestions. Itexaminesawide-rangeofliteraturesrelatedtoagronomy,
urbanagriculture,verticalfarming,androoftopfarming. Italsoreviewsinvolvedtechnologies,current
cultivationtechniques,businessmodels,andanalyzesresearchprojects.
This study evolved from anecdotal observations to systematic examination of involved
technologies, actual and visionary projects of vertical farming. In the preliminary stage, surfing
theInternet(website,blogs,movieclips)excitedandfueledtheresearchbyinformingaboutrecent
projectsthatutilizeadvancedtechnology. Thissparkedsystematicexaminationofgeneric(secondary)
andspecialized(primary)literaturesonverticalfarmingbyusingvariousonlinesearchenginesand
databasesincludingScopus,ProQuest,andGoogleScholar. Researcherscollectedover100sources.
Thesesourcescomprised42%peer-reviewedacademicjournalarticles,28%booksandbookchapters,
6%theses,9%conferencepapers,and15%websites. Mostofthereviewedliteratureisrelativelyrecent,
dating2010–2017. ThereviewedprojectscomemainlyfromNorthAmerica,Europe,andAsia.
Overall, this study adopts a qualitative informative approach. The paper gathers complex
technicalinformationandmakesthemaccessibletothenon-specialists. Collectively,byreviewing,
organizing, and collating information of various sources, the paper hopes to provide a better
understandingofthetheoryandpracticeofverticalfarming.
1.4. WhatIsaVerticalFarm?
Verticalfarmingseekstoensurethesustainabilityofourcitiesproactivelybyaddressingfood
securitytotheworld’sever-increasingurbanpopulation[4–8]. Inprinciple, itisasimpleconcept;
farm up rather than out [8–10]. The body of literature on the subject distinguishes between three
typesofverticalfarming[9–11]. Thefirsttypereferstotheconstructionoftallstructureswithseveral
levelsofgrowingbeds,oftenlinedwithartificiallights. Thisoftenmodestlysizedurbanfarmhas
been springing up around the world. Many cities have implemented this model in new and old
buildings,includingwarehousesthatownersrepurposedforagriculturalactivities[8]. Thesecond
typeofverticalfarmingtakesplaceontherooftopsofoldandnewbuildings,atopcommercialand
residentialstructuresaswellasonrestaurantsandgrocerystores[9,10]. Thethirdtypeofverticalfarm
isthatofthevisionary,multi-storybuilding. Inthepastdecade,wehaveseenanincreasingnumber
ofseriousvisionaryproposalsofthistype. However,nonehasbeenbuilt. Itisimportant,however,
tonotetheconnectionbetweenthesethreetypes,thesuccessofmodestlysizedverticalfarmprojects
andthematurationoftheirtechnologieswilllikelypavethewayfortheskyscraperfarm[9].
Environmentalists, urban farmers, architects, agronomists, and public health experts, among
others,havebeenjoiningthisminirevolutionastheypartnertoworkoutawaytosalvageafood-scarce,
ultra-urbanizedfuture.Awidenumberoftechnologyexpertshaveconvergedontheconceptofvertical
farming, advancing the fields of robotics, aeroponics, aquaponics, and hydroponics. Nonprofits
organizations,aimingtopromoteenvironmentalismandlocaleconomicprosperity,havebeenbacking
the vertical farm concept. Similarly, for-profit ventures that seek to meet the demand for local
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produce have supported this concept. Further, governments looking for ways to boost domestic
foodsecurityhavebeenfundingtheseendeavors. NumerouscountriesincludingKorea,Japan,China,
Germany,theUnitedArabEmirates,China,France,India,Sweden,Singapore,andtheUnitedStates,
haveconvenedtodiscussverticalfarming. Theyhaverepeatedlyendorsedtheconceptasintegralto
thelong-termsustainabilityoftheircities[9].
Theideaofverticalfarmingisnotentirelynew. Examplesofitcanbefounddatingbacktothe
ancienteraintheHangingGardensofBabylon,oneofPhilon’sSevenWondersoftheAncientWorld,
builtaround600BC.In1915,GilbertEllisBaileycoinedtheterm“verticalfarming”andwroteabook
titled“VerticalFarming”. Hearguedthatfarminghydroponicallyinacontrolledverticalenvironment
wouldprovideeconomicandenvironmentalbenefits. Intheearly1930s,WilliamFrederickGericke
pioneeredhydroponicsattheUniversityofCaliforniaatBerkley. Inthe1980s,ÅkeOlsson,aSwedish
ecologicalfarmer,alsoproposedverticalfarmingasameansforproducingvegetablesincities. Heis
knownforhavinginventedaspiral-shapedrailsystemforgrowingplants[4–9]. Aroundtheturnof
thecentury,DicksonDespommier,anAmericanecologist,andprofessorofpublichealth,passionately
revivedtheconceptofverticalfarming. Hedescribedtheverticalfarmas“themasscultivationof
plantandanimallifeforcommercialpurposesinskyscrapers. Usingadvancedgreenhousetechnology
suchashydroponicsandaeroponics,theverticalfarmcouldtheoreticallyproducefish,poultry,fruit,
andvegetables”[7](p.15).Theverticalfarmisconsideredtopromotesustainableagriculturalpractices
morethanthatbyconventionalfarming,whichreferstolargescale,outdooragriculturethatembraces
systems that engage heavy irrigation, intensive tillage and excessive use of fertilizers, pesticides,
andherbicides[5](p. 16).
1.5. WhyVerticalFarms?
1.5.1. FoodSecurity
Foodsecurityhasbecomeanincreasinglyimportantissue. Demographersanticipatethaturban
populationwilldramaticallyincreaseinthecomingdecades. Atthesametime,landspecialists(e.g.,
agronomists,ecologists,andgeologists)warnofrisingshortagesoffarmland[4–6].Forthesereasons,
fooddemandcouldexponentiallysurpasssupply,leadingtoglobalfamine.TheUnitedNation(UN)
estimatesthattheworld’spopulationwillincreaseby40%, exceeding9billionpeoplebytheyear
2050[12]. TheUNalsoprojectsthat80%oftheworld’spopulationwillresideincitiesbythistime.
Further,itpredictsthatby2050wewillneed70%morefoodtomeetthedemandsof3billionmore
inhabitantsworldwide[12]. Foodpriceshavealreadyskyrocketedinthepastdecades,andfarmers
predictthatpriceswillincreasefurtherasoilcostsincreaseandwater,energy,andagriculturalresources
diminish[7–10]. Thesprawlingfringesofsuburbandevelopmentcontinuetoeatupmoreandmore
farmland. Ontheotherhand,urbanagriculturehasbeenfacingproblemsduetolandscarcityandhigh
costs. Wedesperatelyneedtransformativesolutionstocombatthisimmenseglobalchallenge[8–11].
The logic of vertical farming is simple: produce more food on less land [10,11]. The same
rationalethatweusetostackhomesandofficesinlimitedandexpensiveland,suchasinHongKong
or Manhattan, can apply to farming. Proponents of the vertical farm claim that it would create
compact and self-sufficient ecosystems that cover multiple functions, from food production to
wastemanagement. Verticalfarmingcouldenablefoodproductioninanefficientandsustainable
manner,savewaterandenergy,enhancetheeconomy,reducepollution,providenewemployment
opportunities,restoreecosystems,andprovideaccesstohealthyfood. Inacontrolledenvironment,
cropswillbelesssubjecttothevagariesofclimate,infestation,thenutrientcycle,croprotation,polluted
water runoff, pesticides, and dust [12]. As such, indoor farming could possibly offer a healthier
environmenttogrowfood[5,13]. Sinceindoorfarmingoperatesyear-roundandisindependentof
weatherconditions,itcouldalsoprovidegreateryieldsandperpetualincome[14].Furthermore,indoor
farmingprovidesalow-impactsystemthatcansignificantlyreducetravelcosts, aswellasreduce
GHGemissions,bycuttingdownontraveldistancesbetweendistantfarmsandlocalmarket[13,15].
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Also,verticalfarmingcouldignitelocaleconomiesbyprovidingmuchneeded“greencollar”jobsto
urbanareas[5,13].
Importantly,verticalfarmscouldhelpinaddressingtheproblemoffarmlandshortages[4,5,7].
According to the United Nations’ Food and Agriculture Organization, there was 0.42 ha (1 ac) of
arablelandperpersononearthin1961. By2002,becauseofpopulationgrowthandurbanization,
thatnumberhasdroppedbynearlyhalf,to0.23ha(0.5ac)[5]. In2011,theUnitedNationscompleted
aglobalassessmentoftheplanet’slandresources,determiningthataquarterofallarablelandishighly
degraded. Further,since1960,onemillionfarmersintheUnitedStateshavegaveupfarming[5–19].
Today,thecountrysuffersfrom“23millionfooddeserts,definedbytheU.S.DepartmentofAgriculture
(USDA)asurbanneighborhoodsandruraltownswithoutreadyaccesstofresh,healthy,andaffordable
food”[20](p. 32). DicksonDespommierexplainsthatcurrentagriculturalsupplywillsoonbecome
largelyinadequate. Thatis,onaverage,everyhumanbeingneeds1500caloriesdaily,andinorderto
meetsuchdemand,wewillneedtoaddtoexistingagriculturallandanareaasbigasBrazilby2050[7].
1.5.2. ClimateChange
Climate change has contributed to the decrease of arable land. Through flooding, hurricane,
storms,anddrought,valuableagriculturallandhasbeendecreaseddrastically,therebydamaging
theworldeconomy[7,11,12,18]. Forexample,duetoanextendeddroughtin2011,theUnitedStates
lost a grain crop assessed at $110 billion [11,19,20]. Scientists predict that climate change and the
adverse weather conditions it brings will continue to happen at an increasing rate. These events
willleadtothedespoliationoflargetractsofarableland,renderingthemuselessforfarming. Itis
common for governments to subsidize traditional farming heavily through mechanisms such as
cropinsurancefromnaturalcauses[6,21,22]. Furthermore,traditionalfarmingrequiressubstantial
quantitiesoffossilfuelstocarryoutagriculturalactivities(e.g.,plowing,applyingfertilizers,seeding,
weeding,andharvesting),whichamountstoover20%ofallgasolineanddieselfuelconsumptionin
theUnitedStates. Weneedtounderstandthat“foodmiles”referstothedistancecropstraveltoreach
centralizedurbanpopulations. Onaverage,foodtravels1500milesfromthefarmfieldtothedinner
table[8,15]. Inspecialcircumstances—coldweather,forexample—foodmilescanrisedrasticallyas
stores,restaurants,andhospitalsflyproduceinfromoverseastomeetdemands. Onaregularbasis,
over90%ofthefoodinmajorU.S.citiesisshippedfromoutside. A2008studyatCarnegieMellon
concludedthatfooddeliveryisresponsiblefor0.4tonsofcarbondioxideemissionsperhousehold
peryear[23,24]. Thisisespeciallyimportantgiventheincreasingdistancebetweenfarmsandcities
from global urbanization. Sadly, the resulting greenhouse gas emissions from food transport and
agriculturalactivitieshavecontributedtoclimatechange(Figure1).
1.5.3. UrbanDensity
Verticalfarmingoffersadvantagesover“horizontal”urbanfarmingfortheformerfreeslandfor
incorporatingmoreurbanactivities(i.e.,housingmorepeople,services,andamenities)[7]. Research
hasrevealedthatdesignatingurbanlandtofarmingresultsindecreasedpopulationdensity,which
leads to longer commutes. “If America replaced just 7.9% of its whopping one billion acres of
cropandpasturelandwithurbanfarms,thenmetropolitanareadensitieswouldbecutinhalf”[4]
(p.71). Lowerdensitylivingincurshigherenergyuseandgeneratesmoreairandwaterpollution.
The National Highway Travel Survey (NHTS) indicates, “If we decrease urban density by 50%,
householdswillpurchaseanadditional100gallonsofgasperyear. Theincreasedgasconsumption
resultingfrommovingarelativelysmallpercentageoffarmlandintocitieswouldgenerateanextra
1.77 tons of carbon dioxide per household per year” [23]. Despommier details space efficiency of
verticalfarms. Hesuggestedthata30-storybuilding(about100mhigh)withabasalareaof2.02ha
(5ac)wouldbeabletoproduceacropyieldequivalentto971.2ha(2400ac)ofconventionalhorizontal
farming.Thismeansthattheproductionofonehigh-risefarmwouldbeequivalentto480conventional
horizontalfarms[24,25].
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Figure1.Foodtravelsgreatdistancesfromfarmfieldstodinnertable.Themapillustratesthecaseof
thetravelofbasicingredientsofastrawberryyogurtcan(Adaptedfrom[8]).
1.5.4. Health
Conventionalfarmingpracticesoftenstressprofitandcommercialgainwhilepayinginadequate
attentiontoinflictedharmonthehealthofbothhumanandthenaturalenvironment[7,8,10]. These
practicesrepeatedlycauseerosion,contaminatesoil,andgenerateexcessivewaterwaste. Regarding
humanwell-being,theWorldHealthOrganizationhasdeterminedthatoverhalfoftheworld’sfarms
stilluserawanimalwasteasfertilizerwhichmayattractflies,andmaycontainweedseedsordisease
thatcanbetransmittedtoplants[1]. Consequently,people’shealthisadverselyaffectedwhenthey
consumesuchproduce.
Further,growingcropsinacontrolledindoorenvironmentwouldprovidethebenefitofreducing
theexcessiveuseofpesticideandherbicide,whichcreatepollutingagriculturalrunoff[25]. According
toReneeCho,“Inacontainedenvironment,pests,pathogens,andweedshaveamuchhardertime
infiltratinganddestroyingcrops”[25]. Whenexcessfertilizerwashesintowaterbodies(e.g.,rivers,
streams,andoceans),ahighconcentrationofnutrientsiscreated(calledeutrophication),whichcould
disturbtheecologicalequilibrium. Forexample,eutrophicationmayacceleratetheproliferationof
algae. However,whenitdies,microbesconsumealgaeandsuckalltheoxygeninwater,resultingin
deadaquaticzones[8]. “Asof2008,therewere405deadzonesaroundtheworld”[25].
Further, indoor vertical farming employs high-tech growing methods that use little water
(about 1/10th of that used in traditional farming) by offering precision irrigation and efficient
scheduling[25,26]. This can have a significant ameliorative effect since demands on water will
increaseastheurbanpopulationgrows. Agriculturalactivitiesusemorethantwo-thirdsoftheworld’s
freshwater,andfarmersarelosingthebatterforcropwaterbecauseurbanareasareexpandingand
consumingmorewater. Thewatercrisisislikelytobecomesevererasclimatechangecauseswarmer
temperaturesandproliferatesmoredroughts[25].
1.5.5. TheEcosystem
Traditionalagriculturehasbeenencroachinguponnaturalecosystemsformillennia. According
toDicksonDespommier,“Farminghasupsetmoreecologicalprocessesthananythingelse—itisthe
mostdestructiveprocessonearth”[4](p. 7). Inthepasthalfcenturyorso,theBrazilianrainforest
hasbeenseverelyimpactedbyagriculturalencroachment,withsome1,812,992km2(700,000mi2)of
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hardwoodforestbeingclearedforfarmland[4]. Despommiersuggestedthatencroachmentonthese
ancientecosystemsisfurtheringclimatechange. Inthisway,indoorverticalfarmingcanreducethe
agriculturalimpactontheworld’secosystemsbyrestoringbiodiversityandreducingthenegative
influencesofclimatechange. Ifcitiesemployedverticalfarmstoproducemerely10%oftheground
areatheyconsume,thismighthelptoreduceCO emissionsenoughtodevelopbettertechnological
2
innovationsforimprovingtheconditionofthebiospherelong-term. Byeliminatingfertilizerrunoff,
coastal and river water could be restored, and fish stock of wild fish could increase. Wood, et al.
summarize this point by stating “The best reason to consider converting most food production to
verticalfarmingisthepromiseofrestoring[the]servicesandfunctions[ofecosystems]”[26](p. 110).
1.5.6. Economics
Proponents of the vertical farm also argue that it will supply competitive food prices [27].
The rising expense of traditional farming is quickly narrowing the cost gap. For example, when
verticalfarmsarelocatedstrategicallyinurbanareas,itwouldbepossibletosellproducedirectlyto
theconsumer,reducingtransportationcostsbyremovingtheintermediary,whichcanconstituteupto
60%ofcosts[27]. Verticalfarmsalsoutilizeadvancedtechnologiesandintensivefarmingmethods
that can exponentially increase production. Researchers have been optimizing indoor farming by
calibrating,tuningandadjustingawide-rangeofvariablesincludinglightintensity,lightcolor,space
temperature,cropandroot,CO contents,soil,water,andairhumidity[27–29]. Inaddition,vertical
2
farming provides an opportunity to support the local economy. Abandoned urban buildings can
beconvertedintoverticalfarmstoprovidehealthyfoodinneighborhoodswherefreshproduceis
scarce. Additionally,thehigh-techenvironmentofindoorfarmingcanmakeitfuntofarm. Hence,
atechnology-savvyyoungergenerationhasbeenenticedbythepractice,groominganewbreedof
farmers. Further,verticalfarmingprovidesimpetusinthedevelopmentofinnovativeagricultural
technologies. Finally,itcouldreconnectcitydwellerswithnaturethroughtheactivityoffarming[27].
2. High-TechIndoorFarming
2.1. FarmingMethods
Researchers have advanced myriad methods of urban and vertical farming in the hopes of
contributingtosustainablefoodproduction. Advancedfarmingmethodscouldprovidegreateryields
andusefarlesswaterthantraditionalfarming[17,18]. Thedesign,layout,andconfigurationofthese
high-techfarmswouldprovideoptimallightexposure,alongwithpreciselymeasurednutrientsfor
eachplant.Designedtogrowinacontrolled,closed-loopenvironment,thesefarmswouldeliminatethe
needforharmfulherbicidesandpesticides,maximizingnutrition,andfoodvalueintheprocess.Indoor
farmerscouldalso“engineer”thetasteofproducetocatertopeople’spreferences[30]. Researches
intendtodevelop,refine,andadaptthesesystemssothattheycanbeultimatelydeployedanywhere
intheworldandprovidemaximumproductionandminimumenvironmentalimpacts. Theyrepresent
aparadigmshiftinfarmingandfoodproductionandscholarsviewthemassuitableforcityfarming
wherelandavailabilityislimited[5]. Thesesystems(mainlyhydroponics,aeroponics,andaquaponics)
andassociatedtechnologiesarerapidlyevolving,diversifying,andimproving(Table1). Thepaper
explainsthesesystemsinagradualmanner,fromsimpletocomplex.
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Table1.High-TechIndoorFarming.
Farming Common/Applicable
KeyCharacteristics MajorBenefits
Method Technologies
Fostersrapidplantgrowth; Computerizedandmonitoring
Soillessbased,useswateras Reduces,eveneliminates systems;Cellphones,laptops,
Hydroponics thegrowingmedium soil-relatedcultivation andtablets;Foodgrowingapps;
problems;Decreasestheuseof Remotecontrolsystemsand
fertilizersorpesticides. software(farming-from-afar
Avariantofhydroponics; systems);Automatedracking,
Inadditiontobenefits
itinvolvesspraying stackingsystems,movingbelts,
Aeroponics mentionedabove,Aeroponics
therootsofplantswithmist andtalltowers;Programmable
requireslesswater.
ornutrientsolutions. LEDlightingsystems;Renewable
energyapplications(solarpanels,
Createssymbiotic windturbines,geothermal,etc.);
relationshipsbetweenthe Closed-loopsystems,anaerobic
Itintegratesaquaculture plantsandthefish;itusesthe digesters;Programmablenutrient
Aquaponics (fishfarming)with nutrient-richwastefromfish systems;Climatecontrol,HVAC
hydroponics. tanksto“fertigate” systems;Waterrecirculatingand
hydroponicsproductionbeds; recyclingsystems;Rainwater
andhydroponicbedcleans collectors;Insect-killingsystems;
waterforfishhabitat. Robots
2.1.1. Hydroponics
Hydroponics is a method of growing food using mineral nutrient solutions in water without
soil. EncyclopediaBritannicadefineshydroponicsas“thecultivationofplantsinnutrient-enriched
water, with or without the mechanical support of an inert medium such as sand or gravel” [27]
(p.8). ThetermisderivedfromtheGreekwordshydroandponos,whichtranslatesto“waterdoing
labor”or“waterworks”. Theuseofwaterasamediumforcropgrowingisnottotallynew,butthe
commercialintroductionofhydroponicsaroseonlyrecently[28]. TheNationalAeronauticsandSpace
Administration(NASA)researchershaveseenhydroponicsasasuitablemethodforgrowingfoodin
outerspace. Theyhavebeensuccessfulinproducingvegetablessuchasonions,lettuce,andradishes.
Overall,researchershaveadvancedthehydroponicmethodbymakingitmoreproductive,reliable,
andwater-efficient.
Currently,theuseofhydroponicsinindustrialagriculturehasbecomewidespread,providing
several advantages over traditional soil-based cultivation. One of the primary advantages of this
methodisthatitcouldeliminateoratleastreducesoil-relatedcultivationproblems(i.e.,theinsects,
fungus, and bacteria that grow in soil) [28–30]. The hydroponic method is also relatively
low-maintenance as well, insofar as weeding, tilling, kneeling and dirt removal are non-issues.
The hydroponic method also provides a less labor-intensive way to manage larger areas of
production [8,31,32]. Furthermore, it may offer a cleaner process given that no animal excreta are
used. Furthermore,thehydroponicmethodprovidesaneasierwaytocontrolnutrientlevelsandpH
balance. AccordingtoEbbaHedenbladandMarikaOlsson,“Insoil,manyfactors,suchastemperature,
oxygenlevel,moisture,andmicroorganisms,affecthowsoil-fixednutrientsaremadeaccessibleto
plantssincethenutrientsarebeingdissolvedinwaterthrougherosionandmineralization. Therefore,
the hydroponic method may result in more uniform [produce] and better yields, as the optimum
combinationofnutrientscanbeprovidedtoallplants”[30](p. 17).
2.1.2. CylindricalHydroponicGrowingSystems
TheVolksgardenorcylindricalOmegaGardenhydroponicgrowingsystemisarotating-system
technologywhereplantsareplacedinsiderotarywheels. Whenwheelsspin,plantsrotatearound
centralizedinductionlights. Thewheelsrotateonceevery50minusingalow-horsepowermotor(itis
possibletorunthewheelsviawindturbinesandsolarpanels). Inadvancedrotarysystems,the“plants
rotateconstantlyandslowlyaroundthelightsource,andtheirrootspassthroughanutrientsolution
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whentheyreachthebottomoftheorbit. Turningataconstantrateallowstheplantstotakeadvantage
oforbitotropism(basedontheimpactofgravityongrowth)togrowbigger,strongerandfaster”[32]
(pp. 28–29). TheVolksgardensystemalsoprovidesacompactarrangementfortheplants’rootsinrock
wool,therebyallowingtheplantstogrowmorequicklythanintraditionalhydroponics[32].
Importantly, the“Ferriswheels”, canmultiplytheircapacitybyadding“extremeverticality”,
i.e., unit stacking. To appreciate the efficiency of the system experts have noted, “Each cylinder
holds80plants,andsixcylindersarestackedtogetherabout20feethighateachstation”[32](p. 28).
Thisaddsupto480unitsperstationrequiringonly3.4m2(36ft2)ofspace. GreenSpiritFarmsplans
tofit200stationscompactlyinoneofitsverticalfarmstogrow96,000plantsperyear. Forcomparison,
“conventionalbasilgrowersaverage16,000plantsperacre(43,560ft2),lessthan20%oftheproduction
Green Spirit Farms could have in just 7200 ft2” [32] (p. 28). Furthermore, the Volksgarden system
efficientlyusesdistilledwater,requiringone-tenththewaterusedbytraditionalhydroponicsystems.
“Theirdistillationprocessallowsmultiplereusesofwater. Ratherthandiscardingthenutrient-dense
liquidthatremainsaftertheproducehasbeenharvested,itcanbere-distilledandreused”[32](p.29).
Furthermore,theVolksgardensystementailsvirtuallynoevaporationbecausetheliquidreservoir
forthegrowingsystemisclosed. Additionalwatersavingsareprovidedbyharnessingrainwater,
collectivelyminimizingthedemandonmunicipalwatersystems[32].
2.1.3. UltrasonicFoggers
Scientistshavedesignedultrasonicfoggersystemstominimizemaintenanceandmaximizeyield.
Theyenvisionusingthemformyriadhorticulturalapplications,includinghydroponics,toprovide
multiplebenefitssuchas[33]:
• Supplyingupperrootswithnutrientenrichedfogsthatpenetratedeepintoroottissues,keeping
themmoist,well-nourished,andfreeofdecay[16].
• Promotingthegrowthofminusculeroothairs,whichexponentiallyincreasetheroot’sabilityto
absorbwater,nutrients,andexchangegases[32].
• Reducingtheuseofwaterandnutrientsbyupto50%[32].
• Reducingtheneedforbulkyandcostlygrowingmediums[33].
• Efficientlyusingspace,astheunitsarecompactanddesignedtobefedbyaremotelylocated
reservoir[33].
• Byintegratingultrasonicfoggers,hydroponicsystemscomeclosetoaeroponicsystems[33].
However,therearesomeconcernsthatthehydroponicmethodreliesheavilyonchemicalswhereby
allofthenutrientssuppliedtothecroparedissolvedinwater[29]. Ahydroponicsystemisbasedon
chemicalformulationstosupplyconcentrationsofmineralelements[30].Liquidhydroponicsystems
utilizefloatingraftsandtheNutrientFilmTechnique(NFT),andtheylargelyrelyonnon-circulating
waterculture—though, newrecirculationsystemscanbeappliedinNFTtechniques[30]. Further,
some complain that the produce is tasteless because of all the added chemicals in the system and
becausetherootsdonotgetadequateoxygen[30]. Theseshortcomingsarepartiallyaddressedbythe
aeroponicmethod.
2.1.4. Aeroponics
Aeroponicsisatechnologicalleapforwardfromtraditionalhydroponics. Anaeroponicsystemis
definedasanenclosedairandwater/nutrientecosystemthatfostersrapidplantgrowthwithlittle
wateranddirectsunandwithoutsoilormedia[34]. Themajordifferencebetweenhydroponicsand
aeroponicsystemsisthattheformeruseswaterasthegrowingmediumwhilethelatterhasnogrowing
medium. Aeroponicsusesmistornutrientsolutionsinsteadofwater,soitdoesnotrequirecontainers
ortraystoholdwater. Itisaneffectiveandefficientwayofgrowingplantsforitrequireslittlewater
(requires95percentlesswaterthantraditionalfarmingmethods)andneedsminimalspace[34]. Plant
boxescanbestackedupinalmostanysetting,evenabasementorwarehouse.
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Thestackingarrangementofplantboxesisstructuredsothatthetopandbottomoftheplantsare
suspendedintheair,allowingthecrowntogrowupwardandtherootsdownwardfreely.Plantsarefed
throughafinemistofnutrient-rich,water-mixsolution. Becausethesystemisenclosed,thenutrient
mix is fully recycled, leading to significant water savings. This method, therefore, is particularly
suitableinwater-scarceregions. Anadditionaladvantageoftheaeroponicmethodisthatitisfreeof
fertilizersorpesticides. Furthermore,researchhasrevealedthatthishigh-densityplantingmethod
makesharvestingeasierandprovideshigheryields. Forexample,oneoftheaeroponicexperiments
withtomatoinBrooklyn,NY,resultedinquadruplingthecropoverayearinsteadofthemorecommon
oneortwocrops[34].
2.1.5. GrowCube
Recentresearchandtechnologicaldevelopmenttaketheaeroponicsmethodtoahigherlevelof
productivityandefficiency. Forexample,GrowCubehasproposedanewaeroponicprototypethrough
thehigh-techcube,whichcontainsfivelightplasticplatesthatspinviaarotisserie-esquewheeland
arelitbyastripoflight-emittingdiodes(LEDs)thatprovidethenecessarylightforphotosynthesis[34].
Atthetopofthecube,adevicespraysanutrient-richmist. Thecubeanditsdevicesarecontrolledand
managedviacomputerandsoftware,andsensorsinsidethecubecommunicatewiththecomputerto
optimizethemicroclimate. Thecubeisalsopressurizedandequippedwithanultravioletgermicidal
lampandahigh-efficiencyparticulateabsorption(HEPA)filter,aswellas“bug-killingfiltersinthe
pipeswherethenutrientmixesarepumped”[34].
Consequently,themicroclimateinsidethecubeisbug-free,makingitsproducefreeofpathogens.
Remarkably,ITcompaniesaredevelopingspecialappsandfoodgrowingfoodrecipes,increasingly
availableonline.Consequently,theaeroponicssystemandtheentiregrowingprocesscanbeoptimized
remotely[34]. “Whenitcomestimetoplanting,simplystickyourseedsinagrowingmedium...
and download the iOS app. From there, you can select and download a ‘grow recipe’ from the
cloud... Usersarealsoencouragedtotweakandforktherecipesastheyseefit,helpingtoimprove
thegrowingandtooffervariations.Soifyouwantcrisperlettuce,youcanselectthatasanoption”[34].
Furthermore,byconductingtheworkautonomously,thecomputer-controlledenvironmentreduces
humanerrorsandminimizestheeffortofgrowingfood[35].
Withsuchacomputerizedsystem,almostanyonecouldbecomeasophisticatedfarmer. What
ismore,thecomputerizedsystemwillhelpto“engineer”tasteandothercharacteristicsproducing
crispy or spicy produce! GrowCube has managed to produce “herbs, flowers and foodstuffs like
wheatgrass, microgreens, pea-shoots and even 28 heads of lettuce”, and it plans to produce fruits
suchasgrapes[34]. Theprototypeiscostlyandwilllikelybenefitfromeconomiesofscalewhenitis
producedinmasses. Consequently,GrowCubeplanstoexpandtheprojectbyproducinghundredsof
thesehigh-techcubes[34].
2.1.6. SolarAquaculture
Solar aquaculture involves growing high-quality fish protein in small, clean, translucent,
andcontrollablepondsthatareexposedtosunlight. Microscopicgreenalgae(nonfloweringplants
lackingatruestem,roots,andleaves)liveinthepondwiththefishandgrowbyabsorbingnutrients
fromthewater. Inaddition, sunlightthatstrikesthepondhelpsthealgaetogrowandcausesthe
watertobecomewarmer. Fishandalgaegrowfasterinwarmerwater. Thismethodcouldbesuitable
forverticalfarms,enablinghigherratesofproductioninlimitedspaces. Asolarpondthatis1.5m
high,1.5mindiameter(5fthigh,5ftdiameter)andcontains2649L(700gal)ofwatercanproduce
anannualgrowthof18kg(40lb)offish[35].
Inadditiontosupportingfish,solarpondscanserveindirectlyasstorageunitsforsolarheat.
Algae capture about five percent of the entered solar energy while water absorbs the rest (95%).
Thepondmakesaircoolerduringtheday,giventhatmuchoftheincomingsunlightisstoredaswarm
waterratherthanhotair. Incontrast, thepondwarmstheairatnightasitreleasesheat. Assuch,
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heatfromasolarpondcansubstituteforheatingagreenhousewithgas,oilorwoodorelectricity,
therebysavingonenergy. However,thesolarpondrequiresextensivemaintenancebecauseofthefish
wasteandsomeoftheun-eatenfoodthattransformsintowaste. Theseproblemsareaddressedby
closed-loopsystemsandtheaquaponicsmethod.
2.1.7. Aquaponics
Aquaponicsisabio-systemthatintegratesrecirculatedaquaculture(fishfarming)withhydroponic
vegetable,flower,andherbproductiontocreatesymbioticrelationshipsbetweentheplantsandthe
fish. Itachievesthissymbiosisthroughusingthenutrient-richwastefromfishtanksto“fertigate”
hydroponicproductionbeds.Inturn,thehydroponicbedsalsofunctionasbio-filtersthatremovegases,
acids,andchemicals,suchasammonia,nitrates,andphosphates,fromthewater. Simultaneously,
the gravel beds provide habitats for nitrifying bacteria, which augment the nutrient cycling and
filterwater. Consequently,thefreshlycleansedwatercanberecirculatedintothefishtanks. Inone
experimentalproject,aquaponicsconsistingofwetlandpoolscontainingperchandtilapia,whosewaste
providednutrientsforgreens,solvedtheprincipalproblemsofbothhydroponicsandaquacultureas
mentionedabove[36](Figure2).
Figure2.Basicsofanaquaponicsystem(Adaptedfrom[19]).
Researchers envision that the aquaponics system has the potential to become a model of
sustainable food production by achieving the 3Rs (reduce, reuse, and recycle). It offers bountiful
benefits,suchas[36]:
• Cleaningwaterforthefishhabitat;
• Providingorganicliquidfertilizersthatenablethehealthygrowthofplants;
• Providing efficiency since the waste products of one biological system serves as nutrients for
asecondbiologicalsystem;
• Savingwatersincewaterisre-usedthroughbiologicalfiltrationandrecirculation. Thisfeatureis
attractiveparticularlyinregionsthatlackwater;
• Reducing,eveneliminating,theneedforchemicalsandartificialfertilizers;