Duckweed,atinyaquaticplantwithgrowingpotential

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Duckweed,atinyaquaticplantwithgrowingpotential

AresearchonthepotentialapplicationsofduckweedinurbanwatersystemsinTheNetherlands

HenkvandenBerg-3804445-MScWaterScienceandManagementErikvanLidthdeJeude–3716244-MScWaterScienceandManagement

ArneHak–3757994-MScWaterScienceandManagementCaroMooren–3721701-MScSustainableDevelopment:EnvironmentalGovernance

RubenLeendenUijl–5534747–MScSustainableDevelopment:EnvironmentalGovernanceTatiyanaGiomi–4215117–MScSustainableDevelopment:EnvironmentalGovernance

SebastiaanKraaijeveld-5520843-MScSustainableDevelopment:GlobalChangeandEcosystems

StudentsofUtrechtUniversity,course:TransdisciplinaryCasestudy,incollaborationwithKWRandWaterschapDelfland

Client:ir.E.R.(Edwin)deBuijzer,KWR,supportedbyir.A.J.(Albert)Elshof,ORG-ID

Supervisor:ClaireBarnes

Date:November4,2015

Totalwordcount(fromintroductiontoconclusion):19284

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SummaryThispaperevaluatesthepotentialapplicationofduckweedfoundinurbanwaters.ThisresearchisexecutedbysevenmasterstudentsofUtrechtUniversityincommissionofwaterresearchinstituteKWR and the water board of Delfland. Research is conducted bymeans of literature review andcomplemented by expert interviews. In urban waters, intense duckweed cover causes problemsconcerning odor, aesthetics and ecological water quality. Citizens complain to the local waterauthority and municipality about the odor, and the Dutch government is responsible for goodecological quality of thewater. Therefore solutions need to be brought up on how to copewithunwanted duckweed growth. The best solutionwould be to transform the duckweed fromwasteintoavaluableproductandsubsequentlyincorporatethisproductintothemarket.Therearetwobasicwaystodealwiththeproblemscausedbyduckweed:preventionandcollection.Whether duckweed should be prevented or collected depends on the specifics of water bodies,qualityoftheduckweed,andneedsofthelocalauthority.Topreventduckweedseveralapproachescanbeconsidered.Themostusefulpreventionmethodconsistsof loweringthenutrient level inawater body, which can be achieved by dredging the nutrient rich sediment layers. However, theinitialimplementationcostsfordredgingarehigh.Inorderfornutrientreductiontobeasustainableandstructuralsolution,inputsofnutrientsalsoneedtobehalted.Reducingnutrientconcentrationservesawidersocietalgoal,andhencethecostscouldbespreadovermultiplefieldsofinterest(thegoal of overall ecologicalwater quality improvement). Another interesting preventionmethod forduckweed is to increase the flow velocity to the flush the duckweed away.Moreover, duckweedcannotgrowinfastflowingwaters.Thiscanbeimplementedbypumpingortheinstallationofsmallweirs. If such an artificialwatermanagement system is present, orwhen it canbe relatively easyinstalled,thismethodhaslowercoststhandredging.The most suitable collection methods include duckweed screens and other manual collectionmethods,duetotheirhighefficiencyandrelativelylowcosts.Ontheotherhand,onthelongtermthesemanual collectionmethodswillprobablybemoreexpensive than, forexample, theProskimwater skimmer or the Duckweed Guzzler. This is because the Proskim water skimmer and theDuckweedGuzzler arebothmethodswithhigh initial implementation costs, but lowmaintenanceandemploymentcosts.Bothmethodscollectduckweedonarelativelylargescaleand,especiallytheProskimwaterskimmer,canbeusedinmanydifferentwaterbodiesandgradients.Additionally,sizeor other vegetation is no limitations for these methods. However, the suitability of a collectionmethoddependsforalargepartonthespecificsofawaterbody,suchassize,shape,waterqualityand vegetation. Therefore, in order to decidewhichmethod to use the specific characteristics ofeachwaterbodyneedstobeevaluated.Beforedeterminingtheenduseofduckweed(seetheflow-chartfigure5.4)itisnecessarytoanalyzethe level of contamination. Duckweed takes up nutrients and contaminants from the water, andtherefore a primary benefit of this plant is public water purification. As urban water bodies andduckweed are almost always contaminated the potential use for food or animal feed is currentlyslim.According tocurrent legislationduckweedused for foodoranimal feedneeds tomeet strictstandards and duckweed collected from urban water bodies does not meet these standards.According to the researchers, the most useful product of urban grown duckweed is bio-energy,especiallywhenduckweed ishighly contaminated.Wetduckweedcanbeusedwithhydrothermalprocessing,whichhastheadvantagethat lesstimeandcostsareneededtodrytheduckweed.Byhydrothermal processing bio-oil and biogas could be produced. The use of duckweed in biogasinstallationsisalreadytakingplaceandbiogascompaniesshowgreatinterestinthepotentialuseof

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duckweedintheirinstallations.Finally,formildlycontaminatedduckweed,themostsuitableusageofduckweedwillprobablybenatural fertilizer.Thesetypeofproductscanhelpmeetthedemandfor fertilizers and have a higher content of phosphorous and nitrogen than commonly usedfertilizers.

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SamenvattingDitverslagbespreektdepotentielemogelijkhedenmetbetrekkingtothetgebruikvaneendenkrooswat zich bevindt in water in stedelijk gebied. Dit onderzoek is uitgevoerd door zevenmasterstudenten van de Universiteit Utrecht in opdracht van KWR wateronderzoeksinstituut enHoogheemraadschap Delfland. Het onderzoek bestaat voornamelijk uit literatuur onderzoek,aangevuld door interviews met experts. Intensieve kroosbedekking in water in stedelijk gebiedveroorzaakt problemenaangaande stank, uitzicht endeecologischewaterkwaliteit.Omwonendenklagen vanwege de stankoverlast bij de gemeente of waterschap; de Nederlandse overheid isverantwoordelijk voor een goede ecologische waterkwaliteit. Om deze redenen zullen eroplossingen aangedragenmoetenworden hoe het beste om te gaanmet eendenkroos groei. Deidealeoplossingzouzijnomhetkroosomtevormenvanafvalproductnaareconomischwaardevolproductenomditvervolgensopdemarkttebrengen.Erzijntweebasalemanierenommethetkroosprobleemomtegaan:preventieencollectie.Ofhetgeschikterisomkroosgroeitevoorkomenofomhetgegroeidekroosteverwijderenhangtafvanhetspecifiekeoppervlaktewaterlichaam,kwaliteitvanhetkroosenbehoeftevandelokaleautoriteiten.Om eendenkroosgroei te voorkomen kunnen verschillende manieren van aanpak wordenoverwogen.Demeesteffectievepreventiemethodeishetverlagenvandenutriëntenconcentratieinhet water. Dit kan bewerkstelligd worden door middel van het baggeren van nutriëntrijkesedimentlagen. Echter, initiële kosten voor baggeren zijn hoog en om nutriëntreductie eenduurzame en structurele oplossing te laten zijn dient de toevoer van nutriënten in het waterverminderd teworden. Nutriëntreductie dient een bredermaatschappelijk doel dan de preventievan kroos alleen, namelijk de verbetering van algehele ecologische (water)kwaliteit. Kosten voornutriëntreductie zullen dus niet alleen toegeschreven moeten worden aan de preventie vaneendenkroos. Een tweede interessante preventie mogelijkheid is het lokaal versnellen van destroomsnelheid. Dit laat het krooswegspoelen en voorkomt kroosgroei. Dit kan doormiddel vanpompenofhetcreërenvaneenstuwtje.Het isergafhankelijkvan lokaleomstandighedenofdezetoepassing mogelijk is, maar in sommige gevallen kan dit goedkoper zijn dan baggeren ennutriëntenreductie.Demeestgeschiktecollectiemethodenzijnhetplaatsenvankroosschermenenoverigehandmatigemethoden vanwege de hoge efficiëntie en relatief lage initiële kosten. Anderzijds zal op de langetermijn handmatige collectie waarschijnlijk hogere kosten hebben dan, bijvoorbeeld, de Proskimwaterskimmerende‘DuckweedGuzzler’.Dezelaatstetweezijnmethodenmetrelatiefhogeinitiëlekosten,maarhebbendaarentegenlageonderhouds-enarbeidskosten.Beidemethodenzijninstaatkroos op een grote schaal te verzamelen. De Proskim is bijzonder geschikt in verscheidenewaterpartijen en gradiënten. Bovendien vormen schaalvergroting en overige aanwezige vegetatiegeen belemmering voor deze methode. Welke collectiemethode het meest geschikt is voor deverzameling van eendenkroos hangt sterk af van karakteristieken van het waterlichaam zoalsgrootte, vorm, water kwaliteit en overige aanwezige vegetatie. Een heldere afweging van dezekarakteristiekenisnodigomdeuiteindelijkemeestgeschiktecollectiemethodetebepalen.Voordatbepaaldkanwordenwatdebestetoepassingisvanhetverzameldekroos(zieflow-chartinfiguur 5.4) is het belangrijk dat het gehalte van de vervuilingwordt bepaald. Eendenkroos neemtnutriëntenenvervuilendestoffenopinhetwaterwaardoorhetwatergezuiverdwordt,eeneerstepositief effect van eendenkroos. Omdat water in stedelijk gebied bijna altijd vervuild is, is hetongeschiktvoorgebruik indierlijkeofmenselijkevoeding.Huidigewetgevingschrijftstrengeeisenvooraanvoedingsproductenwaareendenkroosuitstedelijkoppervlaktewaternietaanvoldoet.Dit

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onderzoekwijst uit dat demeest geschikte toepassing voor eendenkroos uit stedelijk gebied bio-energieis,ookwanneerhetkrooszwaarvervuildis.Natkrooskanhydrothermaalverwerktwordenmetalsvoordeeldathetdroogprocesmindertijdkost.Bijditproceskanerbio-olieenbiogasuithetkroos gewonnen worden. Het gebruik van eendenkroos in biogasinstallaties vindt al plaats inNederland en bedrijven laten grote interesse zien naar het potentiële gebruik van kroos in huninstallaties. Tenslotte kanenigszins vervuild kroos geschikteworden gemaakt voorhet gebruik alsnatuurlijke meststof. Dit product kan voorzien in de vraag naar meststoffen en heeft over hetalgemeeneenhogernitraat-enstikstofgehaltedandemeestemeststoffen.

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Contents

Introduction...........................................................................................................................................9

1.Methodology...................................................................................................................................12

1.1Generaldatacollection..............................................................................................................12

1.2Theoreticalframework:TransitionTheory................................................................................12

2.2Transitionpathways.......................................................................................................................14

2.Ecology.............................................................................................................................................17

2.1Environmentalconditions&Distribution..................................................................................17

2.2Composition&Contamination..................................................................................................18

2.3Eutrophication...........................................................................................................................19

3.PreventionofDuckweed..................................................................................................................20

3.1Nutrientsreduction....................................................................................................................20

3.2Overshadowing..........................................................................................................................20

3.3Dredging.....................................................................................................................................21

3.3Flushing......................................................................................................................................21

4.Collectionandtransportpossibilitiesofduckweed.........................................................................23

4.1KnowncollectingmethodsintheNetherlandsandinternationally..........................................23

4.2Futureinnovationsincollectionmethods.................................................................................26

4.3Transport(currentandpossibilities)..........................................................................................26

4.4Favorablemethodsforcollectingandtransportduckweedinurbanareas..............................27

5.Productanalysis...............................................................................................................................31

5.1Waterpurification......................................................................................................................31

5.2Uncontaminatedduckweed.......................................................................................................31

5.2.1Feed....................................................................................................................................33

5.2.2Food....................................................................................................................................36

5.3MildlycontaminatedDuckweed................................................................................................36

5.3.1Fertilizer..............................................................................................................................37

5.3.2Soilqualityenhancement...................................................................................................38

5.4HighlycontaminatedDuckweed................................................................................................38

5.4.1Bio-energy...........................................................................................................................38

5.4.2Bioplastics...........................................................................................................................41

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5.5Synthesis....................................................................................................................................42

6.Transitionmanagementandduckweed..........................................................................................44

6.1Landscape..................................................................................................................................44

6.1.1Legislation...........................................................................................................................44

6.1.2Modeofgovernance...........................................................................................................45

6.1.3Sustainabledevelopment...................................................................................................45

6.2Regime.......................................................................................................................................46

6.2.1Stakeholders.......................................................................................................................46

6.3Niche..........................................................................................................................................49

7.Discussion-ManagementadviceandTransitionpathways............................................................52

8.Conclusion........................................................................................................................................54

9.References.......................................................................................................................................55

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ListoffiguresandtablesListoffiguresFigure1 Flowchartduckweedresearch P.10 Figure1.1 Multi-levelinteraction P.13Figure1.2 Transitionphases P.14Figure1.3 Transitionpathwaysandpossibleinfluencingfactors P.15 Figure2 Floatingduckweed P.17 Figure4.1 AProskimduckweedskimmer P.25 Figure5.1 ComparisonofLysineandmethioninecontentofproteinof

varioussourcesP.36

Figure5.2 Roleofduckweedinnitrogencycle P.37Figure5.3 Possibilitiesforduckweedtoenergyconversion P.39Figure5.4 Differentidentifiedprocessestobio-energy Figure5.5 Aflowchartofduckweedproductpossibilities P.43 Figure6.1 Aflowchartwhattodowithduckweed P.46Figure6.2 Waterpurificationprocess P.47Figure6.3 PrimaryenergyuseintheNetherlandspermajorenergyresource

groupP.48

Figure7.1 Flowdiagramwiththepossibilitiesofduckweed P.53ListoftablesTable2.1 Characteristicsofindividualduckweedspecies P.18Table2.2 Potentialduckweedcomposition P.19 Table3.1 Summaryofduckweedpreventionmethods P.22 Table4.1 Summaryofduckweedcollectionmethods P.28 Table5.1 Aminoacidcompositionofbulkproteinofvariouscrops P.32Table5.2 ResponseofTilapiaandfeedutilizationofduckweed P.34Table5.3 Productionlevelsofegg-layingbirdswithduckweeddiets P.34Table5.4 Dailyweightgrainsofcommonducksfedwithduckweed P.35Table5.5 Meanvaluesofgrowthrateandfeedconversionofpigsfedby

conventionaldietandduckweedbaseddietP.35

Table5.6 Differentduckweedprocessesandapplicability P.39

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IntroductionThe Netherlands is known all over the world for its beautiful water bodies. This characteristiclandscapeisuniquetothiscountry,particularly,inurbanareaswherecitiesspacesarealternatedbybuildings,roadsandcanals.Thepresenceofmanywaterwaysentailstheexistenceofmanydifferentplantsthatresidewithinthesebasins.Overtheyears,acertainaquaticplant,commonlyknownasduckweed,hasattractedtheinterestoftheresearchcommunityandwatermanagementauthoritiesduetoitspotentialaswaterpurifiertoolandproductscompound(Iqbal,1999,p.11;Leng,1999). DuckweedisscientificallyknownasthetaxonomicalfamilyofLemnaceae.Itisthesmallestfloweringplantthatfree-floatsonthesurfaceofstillorslowmovingbodiesoffreshwater.Itlivesinnutrient-richenvironments,growsexponentiallyinsize,andhasthepotentialtocompletelycoverthesurfaceof a water body in less than 24 hours (Verma & Suthar, 2015, p.3). One of the particularities ofduckweedisitsabilitytoabsorbnutrients,heavymetals,phenols,pesticides,dioxins,andpathogensfromthewateranditisoftenusedasaremediationmechanismforbasinswithpoorwaterquality(Leng,1999;vanderSpiegeletal.,2013,p.667).Moreover,duckweedisconsideredtohaveahighductility and can be used in themanufacturing ofmany products because of its high protein andstarch content (Verma & Suthar, 2015, p.3). Particularly, in the past years businesses haveincreasingly developed an interest towards this plant, specifically in regards to bio-energyproduction(Verma&Suthar,2015,p.3).Ontheotherhand,ifuncollected,duckweedblockssunlightfrompassingthroughthewater,resultinginareductionofaquaticlife(Leng,1999;vanderSpiegeletal.,2013,p.667).Furthermore, citizens,especially incities in theNorthernandWesternpartoftheNetherlands,haveraisedcomplaintstothewaterauthoritiesandmunicipalitiesconcerningtheunpleasant odor caused by duckweed. Currently Delfland Water Authority (DWA) removesduckweed only when complaints are raised and processes it as waste. Because most of DWA’sincomecomesfromcities,thisorganizationwantstoincreaseitsvisibilityandreturnpartofitstaxrevenue by providing visible community services. Considering themany possibilities of duckweedprocessing,thedrawbacksthatarisefromnotremovingitfromthewaterways,DWAisinterestedinknowingwhethertherearepossibilitiestoturnduckweed“fromtrashintotreasure”. Given the timeathand, this research coversonlypartially thegoals setby the client andaims toanswertheresearchquestion: Inwhatwaycanprevention,collection,andprocessingmethodsofduckweedintheurbanwatersystemsofTheNetherlandsbemanagedto fostera transition fromundesiredwaste toausefulsustainableproduct? The above research questionwill be addressed by integrating the results derived from answeringthesedisciplinarysub-questions:

1. What kinds of duckweed species are known to exist in the urban water systems of theNetherlandsandwhataretheircharacteristics?

2. What are the (possible) preventionmethods used to solve duckweed related problems inurbanwatersystems?

3. Whatarecurrentandpotentialduckweedcollectionandtransportationpossibilities?4. Whatproductscanbederivedfromduckweed?5. Howcanthenichemarketofduckweedtransitionintothemainstreammarket?

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Anoverviewofthestepstakenduringtheresearchisshownintheflowdiagrambelow(Figure1.).Because the topic deals with aspects from various different scientific disciplines, this study isconducted in a transdisciplinary manner where the research team cooperates across disciplinaryboundaries.

Figure1.Flowchartduckweedresearch The different subjects were researched by the students of the specific discipline involved, asindicated in the research phase of figure 1. During the research phase, students from the otherdisciplines commented on the research in order to integrate other viewpoints and ideas into thedisciplinary parts. When these disciplinary parts were completed, they were integrated in theMarket Analysis (chapter 6) using the transition theory as explained in chapter 1. That way, theresultsofthedisciplinaryresearcheswerecombinedusingonetheory.Theoutcomeoftheanalysiswasinturnusedtowriteacombinedmanagementadvice.Thismanagementadviceconsists,amongothers,ofthepotentialstepsthattheclientsshouldtakewhenconsideringutilizingduckweed.Theclientrequestednoadditionalproductoutcomesthanwhatcanbefoundinthisdocument.Chapter1(transdisciplinary)describesthemethodologyandtheoreticalbackgroundusedforthereport.Thegoal set for this researchwillbeachievedby firstanalysing theecologyofduckweed inChapter2(ecology). Secondly, current and potential prevention techniques are evaluated in Chapter 3(ecology/watermanagement).Thirdly,Chapter4(watermanagement)describespossiblecollectionand transportation methods. Afterwards, the potential of duckweed as product compound are

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identified in Chapter 5 (governance) while chapter 6 (governance/transdisciplinary) assessesbranches of the Dutch market where these products might be placed. Finally, in Chapter 7(transdisciplinary)somemanagementadvicesandindicationsonhowtosteertheuseofduckweedtowardsusefulsustainableproductswillbegiven. Clientaffiliation This research is commissionedbyKWRWatercycleResearch Institute,ORG-IDandDelflandWaterAuthority.Thefirstorganisationworkstowardsthegoalofprovidingassistancethatwillsuccessfullyhelpsocietymanagetheirwaters,usingthreedifferentmethods.First,KWRis involved increatingnew knowledge in regards to healthy, sustainable, innovative and efficient tools that will helpadministerwaters. Secondly, theywork as a bridge between civil society, researchers, businessesandpolicymakers. Indoingso,KWRsupports itsfinalgoalwhichconsist increatingaforumwherestakeholderscaninteractanddesignbusiness-likeandcost-efficientpracticalsolutionstoeverydaywater issues, keeping in mind the impact of such solutions on the wider hydrological system.Therefore,KWRencouragesandsupportsdevelopmentofsocietalinnovationsinandaroundwatermanagement(“KWRWatercycleResearchInstitute,”NN). DWAistheresponsiblebodyfordealingwithmanagementofwaterwayswithintheareacomprisedbetweenDelft,Midden-DelflandandTheHague,locatedintheSouth-Hollandprovince.Theboardofthis authority, not unlike municipalities, is directly elected and composed by representatives ofstakeholders relevant in the area (citizens, industry, owners of open land, mainly farmers, andownersofnatural resources).DWAhas threemainmandates:maintainingdamsanddikes,assesswater quality, and control water levels. These functionalities are financed with taxes paid byresidents and businesses of the area DWA manages (“Delfland Water Authority —HoogheemraadschapvanDelfland”NN). ORG-ID is a management and policy consulting firm, mostly active in the area of the physicalenvironment.Thefirmtapsintobroadknowledgeandextensiveexperienceinworkinginthepublicsector. In ORG-ID’s view, policy making is a continuous process that involves many parties andinterests.Cooperationbetweendifferent stakeholders leads tobetter results,notonly in thenearfuture but also in the long run. With this perspective, ORG-ID works on strategic cooperation,programmanagementandorganizationdevelopment.

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1.Methodology

1.1GeneraldatacollectionTheresearchmethodsusedinthisresearchconsistmainlyofliteraturereviewcomplementedwithexpert interviews. For the first part of the report a division is made between different relevantsubjects:theecologyofduckweed,itsprevention,collectionandtransport,andaproductanalysis.For each subject a literature research using scientific databases is done afterwhich articleswereselectedbasedonrelevanceandnumberofcitationsasthisusuallyindicatesquality,aswellastheabstractsaccompanyingthearticles.Usingthesnowballtechniqueduckweedexpertswereselectedforinterviews(Bernard,2011).Thesetupoftheinterviewsweresemi-openwithasubjectlist(Ibid.).The results of the interviews and literature review were combined to overviews of the ecology,prevention, collection and transportation of duckweed and the possible products derived fromduckweed. Because themethodology is explained in this chapter, the following chapters will notdealwithmethodsextensively.

1.2Theoreticalframework:TransitionTheoryAsduckweed isaproductwithhighpotentialbut isnotyet integrated in themainstreammarket,transition theory could be useful for analyzing the current barriers and possibilities of duckweedprocessesvis-à-visotherproductsandprocesses,aswellas toanalyzewhatpossiblepathwaysforduckweedmightentail. Inotherwords,duckweedproductsarenotenteringanemptymarket,butanalreadyexistingmarketfullofothercompetingproducts.Further,thisapproachwasintroducedofficiallywiththefourthDutchNationalEnvironmentalPolicyPlanasagovernmentalpolicy-makingpathway (Loorbach & Rotmans, 2010, p.238). It is believed that this perspective will enableinnovation within the policy arena through the introduction of an experimental attitude lead bygeneralsocietalgainsratherthanstrictgoals(ibid.).According to Rotmans et al., “[a] transition can be defined as a gradual, continuous process ofchangewherethestructuralcharacterofasociety(oracomplexsubsystemofsociety)transforms”andoftentakesanumberofdecadestobecompleted(Rotmansetal.,2001,p.16).Inthiscase,thesub-systemconsistsofwaterqualityandsustainableproductsthatprovideapositivecontributiontosociety.Transitiontheoryassumesthateverytransitioninsocietyisacoevolutioninwhichdifferentsubsystemsshape,andreshape,eachother(Rotmansetal.,2001,p.16;Kempetal.,2007,p.78).Itisespecially important to look at coevolution in regard to governance since it shows that there arecause-and-effectloopsoverdifferentscalesandbetweendifferentsystems(Ibid.,p.79).Any transitioncanbecharacterizedandanalyzedby lookingat thevarious levelsof transitionsizeand speed (Rotmans et al., 2001, p.19). First, there is the niche ormicro level, where individualactorsareinvolvedinthetransitionprocesses,buthavenoimpactonthestatusquobecausetheyaretoosmallandfewinnumberstobeinfluential.Inthisresearchtheduckweedasasourceofnewproducts.Secondly,theregimeormesolevelisthelevelofthestatusquo’sorganizations,practices,ideas,andinteractionbetweenclustersofactorsandlargeorganizations.Hence,thecurrentmarketwhichduckweedwishestocompetewith.Thirdly,thelandscapeormacrolevelidentifiestheentireset of interacting actors, networks, organizations and governments that operate in a context of,amongothers,rules,regulations,ideology,culture,paradigms,andeconomicsituations(Rotmansetal., 2001, p.19). The landscape thus shapes the status quo and the possibilities of duckweedtransitioningintothemarket.Theregimecantrytoimproveitscurrentpracticeswhenconfrontedwith an emerging niche, or can try to use othermeans at its disposal to prevent theniche fromgrowing(Rotmansetal.,2001,p.19).Ifthenichecanresistthesecounterpressures,itcaneventually

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overcome the regime, and become one itself. Themicro level actors can be supported by actorsfrom themeso andmacro levels by providing the circumstances for themicro level actor to beeffective,aslongasthemicrolevelactorisabletoconstructanenduringdesignthatwithstandsthepressures of the regime (Rotmans et al., 2001, p.20). The interaction between the levels abovedescribedcanbesummarizedbythefigure1.1.

Figure1.1Multi-levelinteractionAregimeoperatesina,foritself,logicalmanner.Regimescanbecharacterizedbyhavinganentireset of rules, principles, infrastructure, institutions, knowledge-base, scientific understanding,experiences,practices,andideasthatpushtheoperationswithinthatregimeinacertaindirection(Kempetal.,1998,p.182).Inotherwordsaparadigm.Todivergefromthissetofcriteriaisdifficult,and it is even more difficult to change them. If a regime is based on technology, it is called atechnological regime (Kemp et al., 1998, p.182). These regimes are even stronger because theyaffect theworldoutsideof the regimeaswell. Theyaffectandco-produce socialbehavior,normsand values, and expectations. Through this, additional social barriers are created for niches toemerge.

A transition moves through four transition phases (Rotmans et al, 2001, p.17). First, a pre-developmentphase,wherethestatusquoinasystemismaintained,but,whereonamicrolevel,thefoundations for a large transition are created. Second, a take-off phase, where the status quoprocessesneedtomakespaceforthenewcomers.Third,anaccelerationphase,wherethetransitionis in full swing and continues to gainmomentum by support and benefits from other actors andareasthroughso-calledpositivefeedback loops. If, forexample,atransitionoccurs intherealmofelectricitystorage,thathasapositiveeffectontheuseofsolarpanels.Lastly,astabilizationphase,where the transition is completed and a new status quo is created (Rotmans et al., 2001, p.17)(Figure 1.2). Duckweed is still in the pre-development phase. No large-scale applications on themainstreammarket have been found. However, as is explained in chapter 5, research and small-scaleexperimentsarebeingconductedregardingtheusageofduckweed.

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Figure1.2.Transitionphases(vanderBrugge,2005,p.166)

Transition theory encompasses historical, social and technical analysis through the assessment oftherelationofthreeaboveexplainedlevels,i.e.landscapes,regimesandniches(Foxonetal.,2010,p.1204).Researchhasfocusedonthreemainlinesofanalysis.Transitiontheoryhasfirstbeenusedtoevaluatehistoricaleventsanddynamicsthathavefosteredthetransition(ibid).Asecondpositiontaken by scholars consist in amore practical approach. This consists in developing a governanceprocess that aids to foster a transition through interactive and recurrent interaction betweenstakeholders. This is called ‘transition management’ (ibid). Finally, the third approach aims atdescribing possible ‘socio-technical scenarios’ that analyze how various technological options incombinationwithstrategies,policiesandstakeholders’behaviorsmayconcurtoaidtransition(ibid).Theresearchwill focusonthe lastperspectiveasexplained insection2.2.Theapproachwillallowthisresearchtointegratetechnologicalandsocialscienceanddeveloptransitionpathwaysbasedonaricheranalyticalground(ibid,p.1211).

2.2TransitionpathwaysInordertodescribepossibletransitionpathwaysofduckweedfromnichetomainstreammarket,itis necessary, according to Foxon et al., to undertake three steps (2010, p.1205). First of all,investigatingtheexistingregimeanditsmaincharacteristics,processesanddynamicsthatmayleadto change or stability (Foxon et al., 2010, p.1205). Hence, this research project understands theregimeasthestatusquo:themainstreammarketinwhichduckweedisconsideredawasteproduct.Furthermore, the main actors per product type, their positions, and currently used technologiesmustbeidentified.Aregimedoesnotfunctioninisolation.Externalpressure,aspublicawareness,economic pressure, or international targets, and internal factors, organizational developments,institutionalstructuresormarkets,mayplayaroleindecision-makinge.g.thenicheandlandscape(Ibid.).Figure1.3belowdescribesthisstagebyprovidinganexampleoftheUKenergymarket.

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Figure1.3.Transitionpathwaysandpossibleinfluencingfactors(Foxonetal.,2010,p.1206)Secondly,itisimportanttoanalyzetheniche,whichinthisresearchisthepossibilityofusefulusageofduckweed,indetail(Foxonetal.,2010,p.1206).Itishelpfultolookatthevariousprocessesthatoccur within the niche and how the behavior and development of the nichemight influence theoverallstabilityofthesystem(Ibid.).Hence,thequestionariseswhetherduckweedhasthepotentialto change the regime. The dynamics of a niche are influenced by many different systems anddifferentobstaclesaretobetakenintoaccount.Whenconsideringforexamplethesuccessofurbanfarming,thisisinfluencedbymanyfactorssuchasurbanplanning,governmentregulations,weatherconditions,media outlet, and popular culture. Thus when analyzing the potential of duckweed itmakessensetotakemanyfactors intoaccountaswell. Inthecaseofanewtechnologicalsystem,theinnovationdynamicsplayanimportantroleinthedevelopmentoftheniche(Ibid.).Thewaythetechnological system is organized, what is allowed andwhat is forbidden in terms of innovation,determinespartly,logically,howthenicheactorsbehave.Thetechnicalaspectsofboththeregimeandnichearetakenintoconsideration(Ibid.).Thirdly, it is necessary to analyze how landscapeornichedynamics candestabilize and change aregime(Foxonetal.2010,p.1207).Thereseemstobequitesomedisagreementintheliteratureonthereasonsandanalyzingcharacterizationsofregimechange(Ibid.).Theclaimsdifferfromlookingat the direction of change (inside or outside of the regime) andwhether or not the changewasorchestratedorrandom,totheoccurrenceofexternal/internalshocksthatsuddenlyopenaregimeto outsiders or demands change, or change that occurs through slow internal processes (Ibid.,p.1207-1208). Foxon et al. propose to look at the governance styles of the system and its actorsinstead, in order to see how changes in governance practices can change systems (Ibid., p.1208).Therefore, in this research the landscape will focus on the overarching governance mode, thegeneral social norms and legislation regarding the possible duckweed products and collectionmethods.Inordertoperformtheactualanalysis,thisresearchwillfollowinthestepsofFoxonetal.(2010).The first step of the analysis is to analyze the landscape. The second step is to identify thecharacteristics of the regime in regards toduckweed. For example, that currentlyother resourcesthan duckweed are used for animal feed, energy, fertilizer, soil enhancer and the other products

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discussedinchapter5,aswellasitsothermaincharacteristics.Thirdly,itisnecessarytoidentifythecharacteristicsoftheniche,hencetheduckweedasingredientsfortheproductsdiscussedinchapter5. Taken theaspectsof step1and2 intoaccount, is thereapossibility forduckweedproducts tomoveintothemainmarket,or,howmightduckweeddevelopandwhat influencewouldthishaveon the regime, are questions that need answers These three steps togetherwill form themarketanalysis.

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2.EcologyIt is imperative tounderstandhowandwhereduckweedgrows inordertoassess thepotentialofsustainable duckweed collection and application. Therefore in this chapter sub question 1will beanswered: ‘Whatkindsofduckweed speciesare known toexist in theurbanwater systemsof theNetherlandsandwhataretheircharacteristics?’DuckweedbelongstothebotanicalfamilyofLemnaceae,theyaredividedintofourgeneraLemna,Spirodela, Wolffia, andWolffiella of which, to date, more than 40 species have been identified(Journey et al., 1994). Duckweed species are the smallest flowering plants,withmost being sizedbelowonecentimetreandnotexceedingthree(Maessen,2014).Theirstructurehasbeensimplifiedbynaturalselectiontothebasicsfeaturesnecessaryforsurvival,sincetheplantlacksleafsandstem(Journeyetal.,1994;Lengetal.,1995).Duckweed,indeed,ischaracterizedbyanovoidfrond,whichfloatsonthesurfaceofwaterbasins,andoneormoreroots(figure2)(Journeyetal.,1994;Lengetal.,1995).Therootshavemultiplefunctions,i.e.tocollectnutrientsandtostabilizetheplant.Asthespecies floats on water they are completely dependent on the available nutrients in the basins(Journey et al., 1994; Leng et al., 1995). Duckweedspecies are able to grow in temperatures between 6and33degreesCelsius,buttheyaresensitivetofrost,although,oftensurvivebychangingtoaninactivestate,calledturion,sinkingtothesoilandlayingthereduringthewinter(Roovers,2005,p.7-9).TherefiveindigenousDuckweed species in The Netherlands (i.e. Lemnaminor, Lemna gibba, Lemna trisulca, Spryrodelapolyrhiza andWolffia arrhiza) and others have beenintroduced over the years (i.e. Lemnaminuta,Wolffiacolumbiana and Azolla filiculoides) (ibid). RecentlyinvasivespecieshavebeenbroughttoTheNetherlands,buttheimpactsofsuchpracticesremainunclear(ibid).

2.1Environmentalconditions&DistributionThenaturalhabitatofduckweedconsistsof freshorbrackishwaters.Theyoftendonotsurvive infastmovingwater(<0.3m/sec)andare,therefore,commoninshelteredlagoons(Lengetal.,1995).Moreover,duckweedcanoftenbefoundinstillwaterswithadepthbetweenoneandtwometersand an organic rich soil (Roovers, 2005, p.8). Further, as above mentioned, duckweed livabilitydependsonwatercontents,andthereforethepresenceofthisplantisanindicatorofnutrientrichwaterways (Maessen, 2014, p.2). It appeared thatDuckweed species favor ammoniummore thannitrateasanitrogensource(Roovers,2005,p.9).Finally,thepHvalueofwaterswhereDuckweediscommonly found varies between five and nine (Leng et al., 1995; Roovers, 2005, p.8). Thecharacteristics of several duckweed species common in The Netherlands are shown in table 2.1.DuckweedisgenerallyfoundineveryprovinceofTheNetherlands,although,itisespeciallycommonin the province of SouthHolland, but notwidely spread in Zeeland and Limburg (Maessen, 2014,p.8).

Figure2.Floatingduckweed(www.aquaterralive.com)

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Table2.1.Characteristicsofindividualduckweedspecies

Species Environmentalconditions Characteristics Distributionbyprovince

Wolffiaarrhiza

Shallow,freshandnutrientrichwaters

Sensitivetofrost;notresistantagainstabrackishandsaltenvironment

AlmostonlycommoninSouthHolland

Lemnagibba

Nitrogenandnutrientrichwaters;capabletogrowinfullsunlight;possessesaircabinstofloathigherthanotherduckweedspecies

Formsturionsduringwinter

EspeciallycommoninSouth&andNorthHollandandinpeatareasinUtrecht

Lemnaminor

Foundinthewatercolumn;growsintheshade;diversewaterqualities,canalsogrowinverysmallwaterssuchacartrailsinthemud

Resistanttofrost EspeciallycommoninSouth&andNorthHollandandinpeatareasinUtrechtbutalsocommonintherestofTheNetherlands

Lemnatrisulca

Foundinthewatercolumn;extremenutrientrichenvironment;alsoinbrackishandfreshwaters;cangrowinshadeandinsunlight

Unlimitedgrowthinnutrientrichwaters;lessresistanttowaterpollutionandtroubledwater

EspeciallycommoninSouth&andNorthHollandalsofoundintherestofTheNetherlandssuchasOverijsselandFriesland

Spirodelapolyrhiza

Lesscommon,doesnotindicatenutrientrichenvironment

Formturionsduringwinter

EspeciallycommoninSouthHollandandinlesserextendinNorthHollandandFriesland

Lemnaminuta

Nutrientrich;stillwaterswithadepthofameter;organicrichsoil;shadowtolerant

InvasivespeciesinTheNetherlands;remainsgreenduringwinter

EspeciallycommoninSouthHolland

2.2Composition&ContaminationDuckweed speciesmostly consistofwater.A research in theUnitedStatesondried LemnaGibbashowed that further elements that can be foundwithin this plant consist of crude protein, crudefiber,fatandash(Hillman&Culley,1978).However,thepotentialofthevariousduckweedspeciesisvast.Intable2.2potentialduckweedcompositioniscomparedwiththreeothercrops.Asshownbythiscomparison,duckweedspecieshaveanaverageof37.0%ofcrudeprotein.Thisishigherthancottonseedandpeanuts.Note that all of these crops are grownunderhuman induced conditionsand therefore the numbers are not applicable to natural circumstances. As duckweed has thecapability to take up nutrients and micro contaminants such as metals and dioxins thecontamination level of duckweed is dependent on thewater quality it grows in. Thewater boardNoorderzijlvest for example concluded that the investigated duckweed only exceeded dangerousmercurylevelsbutwasotherwisefine(Hoving&Holshof,2012,p.25-26).ApilotstudybyHolshofet

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al. in 2007 had other results. The duckweed they investigated consisted of dangerous levels ofdioxins and arsine (Hoving & Holshof, 2012, p.25-26). The difference in outcome is probably thecauseofthedifferentwaterqualitiesthesamplesweretakenfrom.Table2.2.Potentialduckweedcompositioncomparedtoothercrops(Hillman&Culley,1978)

Annualtons/acre(%)

Crudeprotein(%)

Fat(%) Fiber(%) Ash(%) Relativeproteinproductionperacre/year

Duckweed(dry) 7.85 37.0 5.0 7.5 11.0 100.0

Soybeans(dryseed)

0.71 41.7 19.2 5.8 5.4 10.2

Cottonseed(dry) 0.34 24.9 24.7 18.2 3.8 2.9

Peanutswithskinandhulls(suncured)

0.70-1.39 23.6 37.9 21.1 3.2 5.7-11.3

2.3EutrophicationEutrophicationiscausedbytheoversupplyofnutrientsinanecosystem.Duringthisprocess,runoffsfromagricultural land, sewage systemsandnot to forget feces fromducks in thewater anddogsnear the water enter water basins (Roover, 2005, p.1). Nutrients from these leakages, such asnitrogen and phosphate, have a positive effect on the growth rate of water plants. Thus,eutrophicationmaycausewaterwaystogetcompletelycoveredbyduckweed.Whenthishappenssunlightisblockedfromreachingdeeperwaters,provokingashortageofoxygenandconsequentlyloweringphotosynthesis rateof underwater plants and reducing the achievementof nutrient richorganic soil(hypoxia) (Maessen,2014,p.2).This in turnhasapositiveeffectonduckweedgrowthensuring a positive feedback loop. Eutrophication can therefore lead to massive destruction ofunderwaterecosystemsasmanyspeciesdonottoleratesuchenvironmentalconditions (Andersonetal.,2002).Concluding,duckweedisafastgrowingaquaticplantcommoninnutrientrichstillwaters.Theyareknowntohaveadverseimpactonwaterqualityasaresultofeutrophication.Removalorpreventionof duckweed is, therefore, needed to counteract these negative effects. Due to its characteristicsandcomposition,duckweedhasthepotentialtobeutilizedandtransformedintodifferentproducts.

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3.PreventionofDuckweedAsmentioned above, duckweed prefers certain environmental characteristics for optimal growth.One of the possible solutions to reduce the negative effects of duckweed and, at the same time,avoidduckweedcollectioncostsistoaltertheaquaticenvironmenttopreventorreducegrowth.Inorder to be implemented, these changes need to be economically feasible and not significantlydamage theecological situation. This sectionprovidesanoverviewof anumberof strategies thatcan be used in order to prevent or reduce duckweed growth andwill provide an answer to sub-question2:‘Whatarethe(possible)preventionmethodsusedtosolveduckweedrelatedproblemsinurbanwatersystems?’Intable3.1themajorfindingswillbesummarized.

3.1NutrientsreductionUnder normal concentrations, all nutrients are used by the larger floating vegetation and plantsattachedtothebottomandnonutrientsareleftfortheduckweedandconsequentlynoduckweedwill grow (Roovers, 2005, p.8).When nutrient concentrations increase due to eutrophication, theamountofnutrientsinthewaterisnolongeralimitinggrowthfactor.Thus,themorenutrientrichthewateris,themoreduckweedwillgrow(Otte&vanHoorn,2014,p.5).Awaytolimittheamountofduckweedgrowthistoreducethenutrientlevelofthewater.Nutrientremovalisconsideredtobe one of themost effectivemethods since duckweed species are unable to store any nutrients,thus,making themhighlydependentonwatercontents (Hovingetal,2012,p.18;Maessen,2014,p.16).Further,thispracticewillimmediatelyeffectduckweedgrowthwithoutsignificantlydamagingtherestoftheecosystem(Hovingetal,2012,p.18).Reducingnutrientsisadifficultprocessanditispracticallyimpossibletodirectlyremovethemfromthewater.Particularly,thenitrogen:phosphateratioisofrelevance.Phosphateisoftenconsideredtobethemainfactorthathindersduckweedgrowth,thus,reducingtheamountofphosphatescanbesufficienttolimitduckweedgrowth(Hovingetal,2012,p.18).Whennutrientconcentrationsarebroughtbelowthreshold,itisimportanttokeepthemstable.InTheNetherlandsthemajornutrientsourceswithinurbanenvironmentsareagricultural inputsfromruralareas,sewageoverflows,andduckfeedleftovers(Roovers,2005,p.33).Furthermore,reducingnutrientsinsurfacewatersmightalsoleadtotheoverallimprovementoftheecological situationofbasins inTheNetherlandsaswellasaidmeeting thegoalsof theEuropeanNitrogen Directive (EU, 1991). When considering nutrient reduction as a possible preventionmethod,therefore,theassessmentshouldalsotakeintoaccountfurtherpositiveimpactsthatmayrisefromsuchintervention.

3.2OvershadowingDuckweed requires sunlight to growandwill hardly, survive in the shadow.One could, therefore,arguethatovershadowingthewatermight reducethegrowthofduckweed (Roovers,2005,p.26).Overshadowingcouldbedonebyplacingplatformsoverthewater.However,thistechniqueishardto implement, not aesthetically pleasing andmight negatively impact the growthof other specieslivinginthosewaters.Plantingtreesonthewaterbanksisanovershadowingalternativethatmightreduceabovementioneddrawbacks.However,nutrientsprovidedbyfalling leavesmightcauseanincrease in the duckweed growth in comparison to the original situation. Despite the shadowingeffect,treesaremorelikelytobeacauseofduckweedgrowththanapreventionmethod(Maessen,2014,p.3).

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Insomewaters,duetosmallcurrentsorwind,duckweedtendstoconcentratenearbends,bridges,indeadendsor in frontofanunderwaterculvert (Roovers,2005,p.26).Asecond,morepractical,optionconsistsofovershadowingonlythelocationswhereduckweedisconcentrated.Thismethodofselectivelyovershadowingmakesthispreventionprocedureafeasibleoption.

3.3DredgingBydeepeningwaterwaysduckweedgrowthcanbereduced(Roovers,2005,p.26).Thismustbedonecarefully when dredging the upper sediment layer because these activities can induce nutrientsseepagefromthesoil(Maessen,2014,p.12).Thiscanincreasenutrientconcentrationinthewaterandsubsequentlyleadtoanincreasedgrowthinduckweed.Itisobservedthattheappearanceofaduckweedcoverafterdredgingisoftentemporarybecausewaterqualitystructurallyimprovesafterdredging (Maessen, 2014, p.12). However, in some cases duckweed concentration increaseswithrespect to other water plants after dredging. This is probably related to the fact that dredgingremovesmostofthewaterplantsattachedtothebottomwhilealotofsmallfloatingduckweedstaybehind(Roovers,2005,p.26).

Secondly,by removing the top layerof thesoil,nutrientconcentration in thewatermightalsobereduced (Roovers, 2005, p.26). This might in turn lead to decrease duckweed growth, furtherdiscussedbelow.Researchhasshownthatdredgingactivitiesinpeatyareashavethebesteffectonreducingduckweedconcentration(Maessen,2014,p.3).

Thirdly,dredging removes theduckweedseeds (turions) fromthebottomof thewaterway.Whensediment removal occurs in late summer or fall, seedswhichwere supposed to hibernatewill beremovedaswellandhenceleadtolessduckweedinsubsequentspring(Roovers,2005,p.3).

3.3FlushingMore flushing of the water system can reduce the growth of duckweed (Roovers, 2005). A firstoption to be considered requires increasing freshwater run through the system in order to raiseflowvelocity.Secondly,whenbasinscanbeartificiallymanagedanditispossibletocontrolseasonalwaterlevels,waterlevelscanbereducedduringa(freezing)period.Indeed,mostduckweedturionscannotwithstand freezing temperatures. Therefore, reducingwater levels and allowing turions tofreeze, can bring duckweed growth almost to zero (Roovers, 2005, p26). Finally, other watermanagementpracticestoreducetheamountofduckweedistoheightenculvertsabovethewaterlevelortocreateasmalloverflowsoduckweedcangowiththewaterflow(Maessen,2014,p.33).SincemostsurfacewaterlevelsinTheNetherlandsareartificiallymanaged,increasingflowvelocityandreduceseasonalwaterlevelsmightbepossibleinsomecases.Feasibilityofsuchpracticeswithincity waters will depend on characteristics of waterways. However, when duckweed is alreadypresentcaremustbetakenthatthisplantisnotflushedtoanotherstagnantwaterbodies.Thebest suggestedpreventionmethodwouldbe to reduce theamountofnutrients in thewater.Initialnutrientreductioncanbeachievedbydredgingthenutrientrichsedimentonthebottom.Asecondadvantageofthedredgingisthatduckweedturionsinthesedimentwillberemovedaswell,which reducesnewduckweedgrowth in thecomingseason.However, inorder to let thenutrientreductionbesuccessful,theinputofnutrientsneedtobereducedaswell.Reducingnutrientinputisdifficult andexpensive toachieveasmany stakeholdersare involved.Nutrient reductiondoesnotonly serve the goal of duckweed reduction, but aims at a better ecological water quality whichserves a broad societal interest. A second feasible prevention optionwould be to locally increaseflowvelocity.Thiscouldbedonebyextrawaterpumpingortheinstallationofoverflows.However,feasibilitystronglydependsonthefacilitiespresentandcharacteristicsofthewaterbody.

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Table3.1Summaryofduckweedpreventionmethods.Method Process Applicability/feasibility Notes

Reductionofnutrients

-Duckweedisverydependentonnutrientconcentrationinwater.Byreducingnutrientcontentduckweedwilldieorunabletogrow.

-Effectiveandimplementableinallwaters.-Difficulttodirectlyextractnutrients.-Indirectextractionbydredgingorduckweedremoval-Preventionof(anthropogenic)nutrientinput

-Sometimesrequiresexpensivemeasures.-Canbeintegratedwithecologicalimprovementofsurfacewater(e.g.Nitrogendirective).-Onlyremovalisnotsufficient,nutrientinputneedstobeloweredsystematically.

Deepening/dredging

-Duckweeddoesnotgrowinwaterdeeperthan1.5m.-Removalofnutrientrichsediments(seenutrientremoval).-Removalofseedsinlatesummer/fallsonoduckweedwillgrowinsubsequentspring.

-PracticallyalmostallwaterwaysinTheNetherlandscanbedredged.-Verysuitableforpeatyareas.

-Dredgingisexpensive.-Dredgingcausesnuisanceforinhabitants.-Whensedimentsareverynutrientrich,mixingcancausemoreduckweedtogrow,althoughthisisatemporalappearance.

Flushing -Flushingawayexistingduckweed-Duckweedfavoursstagnantwaterandwillnotgrowwhenflowvelocityistoohigh.

-Onlypossiblewhenwaterlevelisalreadyartificiallyregulated.Inthesecasespumpingrateswillhavetobeincreased.-Heighteningculvertsabovewaterlevelsoduckweedcanflowaway.-Addingoverflowssolocallyflowvelocityincreasesandduckweedflushesaway.

-Dependsonavailabilityoffreshwater.-Caremustbetakenflushedawayduckweedwillnotconcentrateindownstreamparts.-Dependsoncharacteristicssuchastowhatextentpumpsarepresentanddeadends.

Winterwaterlevelreduction

-Ifwaterlevelislowenoughduringcoldperiods,turionsonbottomwillfreezeanddie,leadingtolessduckweedinsubsequentspring.

-Onlypossiblewhenwaterlevelcanbereducedtosufficientlevel.

Overshadowing

-Byblockingofsunlighttheduckweedwilldie.

-Impracticaltoovershadowcompletewaterways.-Ifpresent,overshadowingofplaceswhereduckweedconcentratespossible.

-Duckweedonlydies;nutrientsremaininwaterwhichcancauseanewduckweedbloomwhenexposedtosunlight.

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4.CollectionandtransportpossibilitiesofduckweedDuckweedisbecomingaprobleminurbanareasmainlyduetotheunpleasantodourresultingfromthedegradationofperishedplants,whichcanbepreventedby regularly removing it.Thischaptertherefore focusesondifferentpossible collectionmethods, performedbyhandormachines. Sub-question3willbeinvestigatedinthischapter:‘Whatarecurrentandpotentialduckweedcollectionandtransportationpossibilities?‘Itwilladdress themaincharacteristicsofeachtechniquebyhighlightingthecosts, timeemployedandcollectionefficiency inpercentagewhich is theamountofcollectedduckweedcomparedwiththetotalduckweedinapond.Acarefulcollectionofduckweedensureshigherwaterqualityandthispracticecouldalsohaveabeneficial impactonthebasinby, forexample,allowing theremovalofwaste out of the water combined with the removal of duckweed (Maessen, 2014). Further, thischapter will indicate possible innovations that could lead to technological advancements withincollectionmethods.FollowingthewaterauthorityofValleiandVeluwe,theparametersduckweedcoverage,reachabilityandmorphologyareofimportance(Maessen,2014).Theseparametersinfluencethetime,costsandthe choiceofpossiblemechanisms to removeduckweed.Collection time is not easily determinedandisdependentonthesize,amountofduckweedpresentandobstaclesimpedingtheaccesstothewaterway. This element has, also, a direct impact on the expense necessary for the collection.Further, considering costs, literature estimates them in different units, i.e. per hour, per size ofremovalorinitialcostsofmachineries.Duetothisissue,comparisonmightbedifficult.Therefore,inregards to timeandcostsanapproximationhasbeenmade.Moreover, it is important tomentionthatwhen considering urbanwaterways, other factors need to be taken into account thatmightlimittheoptionsavailableforcollection.Certaincollectionmethodsaredependentonwaterdepth,e.g.usingboats,andwaterwayssurroundings, includingvegetationonriverbanks, isan importantdeterminantforthecollectionmethodtobeused.

4.1KnowncollectingmethodsintheNetherlandsandinternationallyAccording to Arthur Hagen, a consultant for the city of The Hague and the DWA, both themunicipality and thewater authority areextensivelyusingdifferentduckweed collectionmethodsandworkingonimprovingthesetechnologies(2015).MostcollectionmethodsthatwillbediscussedbelowarecurrentlybeingusedinTheNetherlands.However,theinitialpumpwithculvertandtheProskim water skimmer have not yet been employed by either “Waterschap Delfland” or themunicipalityofTheHague,andaremostlyusedintheUnitedStatesofAmerica(USA).Theselectionofcollectionmethodsbasedonthepertinenceofthetechniques.DuckweedscreenThecompanyBerkhofBVcollectsduckweedfromurbanwaterswiththehelpofduckweedscreenswhichconsistofanettiedtoafloat.Thesenetsarelaidverticallyinthewaterandthefloatispulledtowardasideofthebasinsothattheduckweedcanbecollectedusinglandingnets.Thisapproachisconductedbymanpowerandhasacollectionefficiencyof80%-98%and is timeconsuming.Thismethod is not feasible for water bodies which have an irregular shape and high presence ofvegetation,becausethelargescreencannotreachirregularandvegetatedplaces.Thecostsforthismethodareestimatedaround€200perhourandcanbeconsidered lower in theshort termsincethereisnonecessityforaninitialinvestmentonmachineriespurchase(Maessen,2014,p.25).

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ThecranemethodAnothermethodisusedbyacontractornamedHarryBlokland,wherebyaboatskimstheduckweedfrom the water utilizing a crane with a filter at the bottom to remove the duckweed out of thewater.Thismethod is costlydue theuseofmachineries, thecollectionefficiency is relatively low,70% - 85%, but time is significantly reduced in contrast to manual collection. This method costsaround €110 per hour, for boat, crane and labor. Additional costs of around €722 might beaccountedforthedeliveryofequipmentandtransportofduckweed.(Maessen,2014,p.26).KrooskarperThe company Reijm BV uses a so called “Krooskarper”. Since this method has recently beendeveloped,costsmightbeunreliableandefficiency levelarestillunknown.The“Krooskarper” isamowingboatusedtotrimaquaticplantswhichhasbeenredesignedtoinordertocollectduckweed.ThishasbeenachievedbychangingthesawintoaV-shapedlandingnet.Theduckweediscollectedand stored within the net inside the boat. The boat is unfeasible for shallow waters due to thepropellerbehind theboat. Thismethod is estimated to cost around€200 foronehour (Maessen,2014,p.26-27).DuckweedcatamaranArelatively inexpensivecollectionmethod isdesignedbythecontractorcalledCh.Portengen.Thiscompanydesignedthe“Duckweedcatamaran”,wheretwofloatsareconnectedbyaconveyorbeltthat collects duckweed usingmanpower. Although, thismethod is susceptible for shallowwatersandextremely timeconsuming, ithasa collectionefficiencyof80%and itwill costapproximately€125foronehour(Maessen,2014,p.27).DuckweedwheelA “duckweed wheel”, created by Bom Aqua BV, has a similar design to the previously discussedmethod (duckweed catamaran), where a conveyor belt held by two floats is used to collectduckweed. However, this machine does not require labor and is powered by solar panels. Thismethodisconsideredtobenotveryefficientinthecollectionofduckweedsinceithaslowcollectionefficiency, excessive collection time and a high chance of having power shortages because ofshadowyplacesanddirtysolarpanels(Maessen,2014,p.28).Theonlycostsofsuchmethodcouldconsistintheinitialinvestmentaccountedfor€4000(Maessen,2014,p.28).DuckweedGuzzlerA recently designed method by the ‘Waterschap Rijn en IJssel’ is called a Duckweed Guzzler(‘kroosslurper’).Thismethodconsistsofaboxandapipe.Theboxcreatesorusesapresentgradientofthewaterbodyandwillacceleratethewaterflowinordertocollecttheduckweedintotheboxandtransportitthroughthepipetothebank.However,insomeurbanwatersthereisnogradient,and is therefore createdby theDuckweedGuzzler.Another idea is that apumpcouldbeused tobring in the water into the Duckweed Guzzler. The advantage of a duckweed Guzzler is itstransportability.TheGuzzlercaneasilybetransportedaftercollectingtheduckweed.Moreover,theduckweedcouldbeeasilyremovedfromtheGuzzlerviaaconveyorbelt(Raaphorst,2015,p.10-15).This conveyor belt could transport the duckweed directly in a bag for further purposes. OtheradvantagesofaDuckweedGuzzleraretherelativelyhighspeedofduckweedcollection(apondofabout 1000 m2 is cleaned in 2 days). This method could be combined with solar energy. ThiscollectionmethodisconductedbyBomAquaBV(BomAquaBV.,NN)andwillprobablycostinitiallyaround €20.000,00, which is €5.000,00 for the Guzzler and €15.000,00 for the conveyor belt.However, these machines could be used for more places, so the costs for one-off collectingduckweedwillbemuchlower(BomAquaBV.,NN).

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InitialpumpwithapipeandaculvertTamraFakhoorian,presidentofGreensunproducts,usesaninitialpumpwithapipeandaculverttocollect duckweedand transport it by trucks for furtherprocessing. This pumpcosts about around€2200andharvests800poundsofduckweedinfourminutes.However,thiscollectionmethodcanbestbeusedinareaswithanextensiveduckweedgrowth,e.g.duckweedfarms,becauseinitialcostsaretoohighvis-à-vistheprojectedbenefits(Fakhoorian,2015).Furthermore,thereareuncertaintiesabout the technical aspectsof this design, theefficiencyof the collectionand theperhour costs,whichFakhooriancouldnotdisclose.DuckweedwaterskimmerTheAmericancompanyProskimdesignedaduckweedwaterskimmerwhichpumpstheupperwaterlayerfromasmallfloatingunitinthewatertoanonshorefiltrationunit(seefigure4.1).Thefloatingunitcreatesa“vortexofwater”thatdrawsintheduckweed.Thefloatingunitisconnectedbyhosesto the onshore filtration unit. This unit separates the duckweed from thewater. Thewater flowsbacktothewaterbodywhilethecollectedduckweedstaysontheshore(Proskim,2013).Accordingto their website this installation cost about €5 753. The machine collection time is consideredextremelylong,however,thereisnomanpowerneeded.Additionally,theunitiseasilytransported.

Fig.4.1.AProskimduckweedskimmer(Proskim,2013).

IntensivemanualduckweedharvestingThiscollectionmethod isconsideredpre-emptive,whichentailsthatthefirstharvestedamountofduckweed is lower than when collected at a later stage. However, the unpleasant odor shoulddisappear after this method is applied (Riemer, 1994; Verma & Suthar, 2015). The collection ismostly conducted through the use of landing nets and a boat to reach the further ends of thewaterways(Raaphorst,2015,p.4-9).Anadvantageofthismethodisa lowerwastecontent,asthiscould be separated before collection of duckweed. Since it is difficult to createdmachineswhichseparatesduckweedfromwaste,thepre-collectionseparationmightresultinahighervalueofthecollected duckweed (Hagen, 2015). Therefore the amount of duckweed remaining the ponds is

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sufficient to maintain a high water quality and food for animals, while the bad odor caused byduckweedsurplusisreduced.

The costs of intensivemanual duckweed harvesting in the city of The Hague in a whole growingseasonfromMayuntilOctoberwillbeabout€15876(Raaphorst,2015,p.4-9).Thesecostsincludelabor,travelandcollectingequipmentforanareaof3250m2dividedoverthreedifferentpondsinthe city. This collection results in 60% efficiency with 80% duckweed covering. This collectionmethod is extremely time-consuming. Further, costs are high compared to other, moretechnological,methods.Yet,thismethodcouldbeusedinalmostallurbanwaterbodieswithouttheneedfor largemachineryandmightbeameantocreateemployment. If thismethod iscombinedwithpublicparticipationor,forexample,unemployedcitizens,costswouldbeextensivelyreduced.

4.2FutureinnovationsincollectionmethodsThissectionfocussesondesignsorideasofcollectionofduckweedinurbanwatersdevelopedbytheresearchersofthisproject.Someofthepreviouslydiscussedpreventionmeasurementscouldeasilybecombinedwiththecollectionofduckweedandthuslowertheneedofcollection.Insomecasesthepondsshouldbeadaptedtocreateforexampleagradientinthewaterpondorchannel,suchagradient could easily be used to collect duckweed at a point. Duckweed collection could becombinedwithaculvert,howeverinthiscasetheculvertshouldbelocatedabovethewatersurfaceforapart.Throughthisculverttheduckweedwillbetransportedtoanotherchannelorpond.Iftheculvert contains a net it could capture the duckweed inside the culvert. In this case, the culvertshould be adapted in such away that the collection net could easily be removedwhen it is fullyloadedwithcapturedduckweed.Thenetissituatedinsidetheculvert,sotheonlyworkforcollectingtheduckweedisemptyingthenet(CapelleaandenIJssel,NN).Thismethodwillhaverelativelylowcosts(lowinitialcostsandlittleworkingtimebyemployments)andthecollectiontimewilldependonthecurrentinthechannelorpond(willprobablybeseveraldays).Anothercollectingmethodcouldbedesignedfromvalvesinurbancanals.Thesecanalsalreadyhavesuchvalvesforpreventingduckweedtransportationtoothercanals.Thesevalvesensuresapropertransportofwaterbypreventingvegetationorwaste(atthesurface)tomigratetotheothercanals.If thesevalveswerecombinedwith“bigbags”asdiscussed insection4.1 (Raaphorstetal.,2015),then duckweed could be collected. This collected duckweed will be of a low quality because itincludeswaste.However,thismethodcouldbeeasilycreatedandappliedincities,hencereducingtheamountofduckweedandtheassociatedodor.Thecostsforthismethodwillberelativelylow,likethemethodwithaculvert,alsothecollectiontimewillprobablybeseveraldays.Inalmostallpondsandchannelsthereisaflow,thereforetheduckweedinoftensituatedtogethercausedbytheflow.Ifitispossibletocreatearoofabovethispointwithalotofduckweeditwouldbeapotentialmethodtopreventduckweedorcollectitaftertheduckweeddies.Theroofwillcauselesssunlight, thereforetheduckweedwilldie. Ifduckweeddies itwilldry, therefore it iseasier tocollectandtransport(weighsless).Thismethodwillberelativelycheapandtheduckweedcouldbecollectedinafewhours(Nieuwenhuizen,2010).

4.3Transport(currentandpossibilities)Whenduckweedisusedforfurtherprocessingorgoingtoawastedump,itneedstobetransported.Transport costs, energy useGHGemissions and scale have to be considered. These issueswill beassessedinthecurrentandpossibletransportwaysfortransportingduckweed.

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Duckweediscollectedinthegreenstate(wetduckweed).Transportingwetmatteriscostlyasfreshduckweedconsistofabout92-94%ofwater(Lengetal,1995).Thereforetheenergyrequiredtodryfreshduckweedishighandthedrymatterwillonlyconsistofasmallpartoftheoriginalduckweed.Thewetterduckweedis,themoreenergyisneededtodryit.Dryingcanbedonebygasheatingorpressing. In research done by Holshof et al. (2009) fresh duckweed was transported to a dryingfacilitywherein30hoursduckweedwasdriedat40degreesCelsiusto90%drymatter(Holshofetal, 2009, p.11). They argue that dryingwill be too expensive to turn it into a competitivemarketproduct.Moreover, toomuchenergy is needed for this process, therefore it is not sustainable.Abetterprocess,accordingtothem, ispressingthewateroutoftheduckweed(Holshofetal,2009,p.11). This reduces thewater content and consistsof the simple stepofpressing thewetmatter.Other research indicates that pressing duckweed could reduce the water content with 50%(Nieuwenhuis&Maring,2009,p.25). Itmightbeanoption to leave thecollectedwetbiomass forsome days on the collection site, in this way also a lot of water could be lost before transport(dependingontheweatherandsiteavailabilities).Todesigngoodtransportoptions,oneneedstohaveinformationaboutbiomassquantities.This isnot only useful for the design of transport, but also for product/processing possibilities. It is,unfortunately, difficult to know how much biomass actually is collected as it depends on thethickness of the duckweed layer in the water, the collection method and the surface area. Forexample considering the thickness of the biomass layer, it was found that when using cultivatedponds,therewouldbe500g/m2freshduckweedbiomass(Derksen&Zwart,2010,p.12).Butsuchanamountoffreshduckweedcouldnoteverywherebeharvested.Research papers about transport costs (also in terms of energy and GHGs) of biomass were notfoundtobeapplicabletothisproject.Formorecompletemodellingofthetransportofbiomasstoabiorefinery,theIBSALmodelisadvised.Thismodelcanmakeasimulationofthewaybiomassgoesfromthefieldtoabiorefinery.Itestimatesthecost,thegreenhousegasemissionsandtheenergyinputneededforcollectionandtransport(Kumar&Sokhansanj,2007).

4.4FavorablemethodsforcollectingandtransportduckweedinurbanareasInTable4.1anoverviewofthedifferentcollectionmethodsaregiven.Theyareassessedbasedonthefollowingparameters;scale,waterquality,costs,executingauthority,transport,collectiontimeandspecials.First,scale.Thisparameterreferstothesizeofthewaterbodyusedforcollection.Thescalerangesfromsmall,mediumand large.unfortunately,exact sizes (in squaremeters) couldnotbedefined.Second,waterqualitywhichreferstothestateofthewaterqualityafterthecollection.Third, thecosts refer to the costs of the collection method in Euro’s. If precise costs are not available,estimationsaremade.Thecostsforpurchasingacertainmachinearereferredtoaspurchasecosts.Costsforstartingacollectionmethod(withoutpurchase)aredefinedasinitialcosts.Othercostsarerepresentedinthetableperhour.Fourth,theexecutingauthorityreferstotheresponsiblepartyforexecuting the collection, e.g. specialized firms or water authorities. Fifth, transport refers to thestateofduckweedduringtransportation.e.g.greenstateordry.Sixththecollectiontimereferstheamount of time used during the collection, estimations aremade, based on collection technique.

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Last,‘specials’isnotanactualparameterbutshowsspecialinformationaboutthecollectionmethodthatcanbeuseful.Table4.1.Summarizingtableforduckweedcollectionmethodsandtransportationinurbanareasbasedonliteratureandexpertopinionsfordifferentparameters(LWA:LocalWaterAuthority).

Parameters

Collectionmethods

Description Scale Waterquality

Costs Executingauthority

Transport

Collectiontime

Specials

Duckweedscreens,manually

Anettiedtoafloat,laidverticallyinthewaterandispulledtothesideofabasin

Medium Improvedafter

200perhour

BerkhofBV Tippertruck

Fewhours

Cranewithascreen

Aboatskimstheduckweedfromthewater,utilizingacranewithnettedbottomtoremovetheduckweed

Medium Mediumimprovementafter

720initialcost+110perhour

LoonbedrijfHarryBlokland

Truck Fewhours Oftenused

Krooskarper AboatwithaV-shapedlandingnet

Medium Mediumimprovementafter

200perhour

FirmaReijmBV

Truck Fewhours

SpecialCatamaran

Twofloatsareconnectedbyaconveyorbeltthatcollectsduckweed

Large Littleimprovementafter

125perhour

LoonbedrijfCH.Portengen

Truck Days

Duckweedwheel

Aconveyorbeltheldbytwofloatsisusedtocollectduckweed,poweredbysolarenergy

All Littleimprovementafter

4000+ LWA TruckBigBags

Weeks UnmannedSolar

Duckweedguzzler

Aboxconnectedwithapipe,createsacurrentinawaterbodytocollecttheduckweedintothebox

Large Improvedafter

20.000purchasecosts

WaterauthorityRijn&IJssel

Truck Days

Pumpandculvert

Aninitialpumpconnectedwithapipe

Largepreferably

Improvedafter

2000+ LWA Truck Days

Manually(nets)

Collectionconductedthrough

Small Improvedafter,

16.000per

LWA/civilians

Truck Days

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theuseoflandingnetsandaboattoreachthefurtherendsofthewaterways

separatewastebyhand

season

Proskim Pumpstheupperwaterlayerfromasmallfloatingunitinthewatertoanonshorefiltrationunit

Smalltomedium

Improvedafter,separatewaste

5000+purchasecosts

LWA Truck Daystoweeks

Newdesign

This sectiondetermines themost recommendedcollectionmethods,basedon theaboveanalysis.TherecentlydesignedProskimwaterskimmershowsa lotofpotential.Whilecurrently itdoesnotcollectduckweedso fast, in the future it could,however,becomea suitablemethod. If thewaterskimmer would be further developed, especially on reducing collection time, this method wouldbecome more suitable. Furthermore, duckweed screens, manually collection and the duckweedguzzleraresuitablemethodsaccordingtotheircollectiontime,efficiency,scaleandcomfortabilityofcollection. All methods have benefits and drawbacks, based on the place of utilization. Mostimportantistofittherightcollectionmethodtothesite.

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LowbudgetoptionsThe most suitable methods for a low budget are probably the duckweed screen and manualcollectionmethods, caused by their high efficiency and relatively low costs. But on a longer timespan these manual collection methods will probably be more expensive than for example theProskimwaterskimmerortheguzzler,becauseaskimmerandaguzzlerarebothmethodswithhighinitialcostsandlowercostsformaintenanceoremployments.LongtermoptionsFor a higher budget the duckweed guzzler and Proskimwould be preferred, due to the relativelylarge collection scales and the lessmanpower that is needed. Another advantage of the Proskimmethodisthatitcouldbeusedinallpossiblewaterbodiesbecausegradient,sizeorvegetationarenotanissueforthismethod.ConclusionThe above discussed methods are all measures developed specifically for duckweed collection.However,thesemethodsoftenhavehighinitialinvestmentsandmaintenancecostswhichhavenotalways been accounted for above. A seconddisadvantage of someof the collection techniques istheir low collection efficiencywhich is an essential parameter to determinewhether amethod isuseful.Thirdly,efficiencylevelsofeachmethodmight,also,beaffectedbyirregularbanksandthehighpresenceofvegetation.Finally,thesemethodscouldhaveharmfuleffectsontheenvironmentand could negatively affect water quality (Maessen, 2014; Raaphorst, 2015; Nieuwenhuis andMaring,2009).Themethodswhich are shown in table 4.1 and notmentioned in the low budget and long termoptions are not directly recommended for collecting duckweed, butmight be suitable for certainspecificplaces.Inshort,themanuallycollectionmethodsareusefulforalowbudgetscenario.TheProskimmethodandtheguzzleraremorefeasibleforahigherbudget,becauseitrequireslessworkandincourseoftimeitwillbecomelessexpensivethanmanuallycollection.

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5.ProductanalysisMany studies have, proven the capacity of duckweed to absorb nutrients, particularly, nitrogen,phosphorus,calcium,sodium,potassium,magnesium,carbonandchloride,fromsurroundingwaters(Cheng&Stomp,2009;Lengetal.,1995;Leng,1999;vanderSpiegeletal.,2013;Xuetal.,2012).Thiscapacityhasbeeninvestigatedasamethodofwastewatertreatmentandhasbeenproventobequitesuccessful(Journeyetal.,1994;Lengetal.,1995;Leng,1999;vanderSpiegeletal.,2013).However,thisabilitymighthavesomedrawbacksdependingontoxicitylevelsofwaterbasinswhereduckweedhasgrown.Heavymetals,phenols,pesticides,dioxins,andpathogensaccumulationposea great danger when further processing the duckweed, particularly when this plant enters thehuman food chain system (Leng, 1999; vander Spiegel et al., 2013). Therefore,dependingon thecontaminationof thewaters and subsequently theduckweed, there aredifferent destinations forthis plant. This chapter will answer sub-question 5 and give a broad description of possibleduckweedderivedproducts. Itwill, first,analyzewaterpurification,which isaserviceprovidedbythisplantbeforeanyotherutilization,and, later,allthepossibleproductsbasedoncontaminationlevels.

5.1WaterpurificationDuckweedcanbeusedasapurifierwhenthewaterissufferingfromeutrophication(Niewenhuis&Maring, 2009, p.10; Xu et al., 2012, p.592). Currently, eutrophication is prevented by activatedsludgeswhichareusedtoremovethesenutrients.Unfortunately,theyarecostlyandtechnologicallycomplex. Duckweed could help organizations to reach theirwater quality targets in the followingway:Due to the fast growth of duckweed, water purification can be done in the form of targetingnutrients, or be employed to reduce pollution from metals (Niewenhuis & Maring, 2009, p.32).Duckweed is relatively resistant tometals, and, therefore, able to reducemetal pollutionwithoutdying itself (Ibid.,p.32). In Figure 5.1 duckweeds tolerance levels to heavy metals are shown.Duckweedalsotakesphosphorusandnitrogenoutofthewater.Thenitrogenisfirstconvertedintoammoniaandthentakenupbytheroots.Oneofthebenefitsofduckweedisthatitbetteradsorbsphosphorus than algae do. Duckweed can remove 30-90% of the phosphorus (Chen et al.,2012).Moreover, it transformsthenutrients inproteinandstarch (Zhouetal.,2015p.550).Additionally,the duckweed roots host bacteria which further absorb waste nutrients (Nieuwenhuis &Maring,2009, p.32). Unfortunately when the water is too polluted, this purifying function has theconsequence that the excess duckweed cannot be used as food or feed. The heavymetals couldaffectthemetabolismoforganisms.Purification could be used in both open and closed (waste)water systems (Niewenhuis&Maring,2009p.33).Forexample,inapurifierorditches.Theexcessduckweedcanbecollectedandusedforbioenergy.Anotherbenefitisthatthereisalmostnoprocessingoftheduckweedneeded;itcanbeusedwet.

5.2UncontaminatedduckweedIn the last years, researchers have turned their attention to duckweed in light of new challengesposedbyagrowingpopulation,theincreaseinconsumptionofanimalsproteinregisteredinthelastdecades,andtheimpactofthehumanfoodsystemontheenvironment(Leng,1999;vanderSpiegeletal.,2013).Animalproteinconsumptionaccountsforupto40%ofthetotalhumanintakeandthe

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FoodandAgricultureOrganization(FAO)foreseesarapid incrementby2050followingthecurrenttrends (Leng, 1999). Given the above challenges, there is a growing need to introduce novelproducts,suchasduckweed,fortheproductionofanimalsproteinsthatarecheaper,healthierandmoresustainable(vanderSpiegeletal.,2013,p.2).

It is of great relevance to take into consideration the protein output per hectare of duckweed incomparisonwithcurrentlyusedplantproteinsourcesforbothfeedandfood,suchassoy,grainsandlegumes.Literaturestudiesondryweightduckweedreportupto3000Kg/hectare/yearofproteincontents(Cheng&Stomp,2009;Journeyetal.,1994).Incontrast,proteinproductionofothercropsismuchlowerrangingfrom300Kg/hectare/yearforsoybeanto70Kg/hectare/yearforriceand180Kg/hectare/year for maize (Cheng & Stomp, 2009). For these reasons, duckweed seems to be aviableoption tobeconsideredwhenaddressingalternativeprotein sourcesandnewstrategies tofosterfoodsecurity(Leng,1999).

Thehighproteincontentofduckweedrendersitapromisingreplacementofsoybeaninanimalfeedproducts. Protein content of dry biomass can be between 15% and 45%, depending on species,strainwithspeciesandgrowingconditions(Cheng&Stomp,2009;Xuetal.,2012).Particularly,ithasbeen found thatduckweedcan reacharound40%ofproteinwithahighbiological value inwaterbasins with 10-30 mg NH3-N/litre (Leng et al., 1995, p.7). These values are similar to proteincontents yielded by soybean, which range between 33 and 49%, also depending on species andgrowing condition (Cheng& Stomp, 2009). High protein values pertain that amino acids qualitiescontainedintheplantcloselyreflectthenecessaryrequirementsforanimalconsumption(Cheng&Stomp,2009;Xuetal.,2012).Table5.1comparesaminoacidcontentsofthreeduckweedspecies,S.polyrrhiza, S. punctata, and L. gibba, rice, corn glutenmeal, peanut, soybeanmeal andmilkwithproteinrequirementsforchickenfeed.Table5.1.AminoacidcompositionofbulkproteinofLemnaceaespecies,grains,legumes,andcasein(Cheng&Stomp,2009)

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Throughtheanalysisoftable5.2, it isevidentthatthecontentofaminoacid induckweedspeciesare lower than the ones contained in soybeanmeals. On the other hand,many researches haveindicatedthehigh impactofgrowingconditionsonpercentageofproteinspresent intheseplants,withvaluesincreasingfromto25%upto50%perindividualaminoacid(Cheng&Stomp,2009).Inaddition, larger yields harvested that the duckweed is able to produce, render this plant highlycompetitive(Lengetal.,1995;Leng,1999).Finally,one lastelementneed tobe taken intoaccountwhenconsideringduckweedasapossibleprotein source for animal feed and human consumption: toxicity. Firstly, in addition to thecontaminantssuchasheavymetals,phenols,pesticides,dioxins,andpathogens, ithasbeennotedthat significant levels of oxalic acid can be found in the genera Spirodela and Lemna, both incrystallized and soluble forms. This compound might be toxic to animals when ingested in highconcentration, although no studies have shown contraindication given by duckweed animal feedcontaining oxalic acid (Cheng & Stomp, 2009; van der Spiegel et al., 2013). Concerning humanconsumption,calciumoxalatecontentsofduckweedneedtobemonitoredtohighlightanypossibletoxicity. However, recent studies have argued that oxalate helps urinary excretion particularly inindividuals suffering from stones (Cross, 2011). For these reasons, duckweed collected for urbanwaterwaysmightnotbesuitableforeitheranimalfeedorhumanfoodasthesetypesofoutcomescanonlybeachievedfromplantscultivatedinhighlycontrolledsettings(Maessen,2014).

5.2.1FeedDuckweed could be a viable source to produce feed and feeding supplement for animals. Manystudieshavebeencarriedout regardinganimals suchas fishes,dairycows,pigs, sheep,goatsandpoultry, and have shown that proteins intake can be partially or totally substituted by duckweedwithoutimpedinggrowth(Cheng&Stomp,2009;Journeyetal.,1994;Xuetal.,2012).FishDuckweedasfishfeedisthemostwidespreadutilizationofthisplant,sinceitcanbeusedinagreenstateandisverysuitableforbothherbivorousandomnivorousanimals(Iqbal,1999,p.57;Journeyetal.,1994,p.18).Commonly,proteinfeedwithhighbiologicalvalueareveryexpensiveandcannotbesupportedby fish farming.Duckweed is locally available and a low cost solution for fish intensiveaquacultures(Lengetal.,1995).Manystudieshavedemonstratedthattilapiaandcarpsfarmscanbe sustained with the use of duckweed balancing feed, fertilizers input, fish density and oxygen(Cheng&Stomp,2009; Iqbal,1999,p.57; Journeyetal.,1994,pp.18–19).Otherpilotexperimentshave shown thatadietary inclusionofSpirodelapolyrrhizaup to30% isefficiently converted intolive-weight as displayed in Table 5.2 (Balogun& Fagbenro, 1995, p.316).More recent researcheshave indicated that a diet containing sole duckweedmight be too low in carbohydrates and fatscontent,thus,suggestingacombinationof50/60%duckweedwith50/40%ofcarbohydratesandfatrichfeedforabalanceddiet(Iqbal,1999,p.58).

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Table5.2.ResponseofTilapiaandfeedutilizationofduckweed(Balogun&Fagbenro,1995)

PoultryDuckweedhasalsobeenwidelyrecognizedtohaveagreatpotentialinpoultrydiets.Itcouldreplacealfalfa(Lucerne)asaproteinsource(Lengetal.,1995,p.9).Birdsfedwithupto25%ofdehydratedduckweed have shown a greater increase inweight gain than those fedwith conventionalmeals(Iqbal, 1999, p.59; Leng et al., 1995, p.9). Furthermore, the high content of carotene and thepigmentxanthophyllreflectswithineggsyolkscolorandnutritionalvalues(Iqbal,1999,p.54).Table5.3showsweightincreaseandeggqualityinpoultryfedwithduckweedmeals.Table 5.3. Production levels of egg-laying birds at 18weeks on conventional base diet containingvaryingproportionsofdehydratedLemnagibbameal (33%Nx6.25 inDM).Metabolizableenergyandproteinintakewereconsistentacrosstreatments(Lengetal.,1995)

Various studieshave indicateddifferent responsesdependingon thedifferentLemnaceaeusedassubstituteandtheirprotein/fiberratio inchickendiets(Iqbal,1999,p.60;Lengetal.,1995,p.9). Ithasbeendemonstratedthatincreasingthepercentageofdriedduckweedintegrationwithinyoungbroiler chickens’ diets negatively impacts their growth, while older birds maintained significantweightgains(Hausteinetal.,1992,p.334;Lengetal.,1995,p.9).Therefore,care isrequiredwhenintegratingduckweedwithinyoungerchickensfeed.

ThereisevidencefromTaiwanandBangladeshthatducks,instead,caneatfreshduckweedreadilyfedordirectlycollected(Iqbal,1999,p.60).Furthermore,Menetal.demonstratehowduckweedisaviablesubstituteofsoybeansinduckfarmingasshownbyTable5.4.Commonducksareunaffectedintheirgrowthrateandthissolutionisbelievedtoreducethecostsoffeedbyatleast13%(Menetal.,2001,p.1746).

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Table 5.4. Daily weight gains of common ducks fed increasing percentage of duckweed asreplacementforsoybeans(SB)(Menetal.,2002,p.1744)

SwineIn regards to swine feed, the information available from literature is highly contradictory (Iqbal,1999, p.59; Leng et al., 1995, p.10). Which could be explained by little available research. Yet,farmersinmanycountrieshaveincorporatedduckweedtoswinemeals(Leng,1999).Hausteinetal.(1992),asquotedbyLengetal. (1995,1999)and Iqbal (1999),reportasignificantdecrease in liveweightgainwithan increaseof fedduckweed.However, it isnecessary to take intoconsiderationthat in this pilot the quality of duckweed was poor (23% proteins and 7.5% fibre content), thetoxicitylevelwasnottestedandtheyoungageoftheanimalsmighthaveplayedarole(Leng,1999).Vanetal. (1997)andHang (1998) showthat replacing7%of thedriedmatterof the swinemealsconstitutedbysweetpotatovineswith5%duckweedatagreenstate,liveweightgainedisgreater(see Table 5.5).Many authors agree on the necessity to further research in regards to duckweedintegration into swine feed, particularly in regards to the possibility of using freshly harvestedduckweedratherthandehydrated(Hang,1998;Iqbal,1999,p.59;Lengetal.,1995,p.10;Leng,1999;Vanetal.,1997).Table5.5.Meanvalues forgrowth rateand feedconversion inpigs fed conventional (control)dietandduckweedatagreenstatereplacingthesweetpotatovines(DW)(Hang,1998).

RuminantsAsforpigs,thereisnotanabundanceofstudiesinregardstoruminants,although,someresearcheshavebeen carriedout for cattle and sheep (Iqbal, 1999,p.60; Lenget al., 1995,p.10). Lenget al.(1995)arguethatduckweedmaynotmakeasubstantialcontributiontotheaminoacidabsorbedbythe animals since proteins might be fermented in the rumen and difficult to be protected fromdigestioninthefirststomach.Nevertheless,researchconductedtodateshowthegreatpotentialsofduckweed integration within ruminants’ meals. Russoff et al. (1977, 1978), as reported by Iqbal(1999), foundthatduckweeddidnotalter thetasteofmilk inHolsteincalves.Furthermore,cattlefedwithamixtureof67%duckweedand33%cornalmostdoubledtheirdailyweightgain,from0.5Kg to 0.94 Kg (Iqbal, 1999, p.60). Finally, it has been hypothesized that approximately 3 ha of

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duckweed cultivation could feed up to 100 dairy cows and increase their milk production (Iqbal,1999,p.60;Leng,1999).Allthesestudieshavebeenperformedusingdriedduckweed.

5.2.2FoodIn Myanmar, Laos and northern Thailand the duckweed specie Wolffia arrhizal is part of thetraditionallocaldietandisconsideredverynutritious.Itisconsideredafoodfor“poormen”andiscultivatedmainlyinruralenvironments(Iqbal,1999,p.56;Leng,1999).Duckweedhasbeenavalidsourceofminerals andgreenvegetables in these regions,particularly throughout thedry seasonswhensuchresourcesareveryscarce(Leng,1999).Remarkablythispracticehasnotspreadtootherareas of the world. This may be because of the high content of oxalic acid in some species ofduckweedaffecting its taste,and thedifficulty in separatingworms, snails,protozoa,andbacteriafromthisaquaticplant(Iqbal,1999,p.56).

Duckweed proteins and its amino acid contents closely reflect animal proteins. Based on FAOnutritionrecommendation,duckweed,consideringitscontentsoflysineandmethionine,couldbeaviable complement to grains diet in human consumption especially in regions where there is adeficiencyinproteinsintake(Table5.6)(Iqbal,1999,p.56;Journeyetal.,1994,p.13;Leng,1999).

Figure5.1.Comparisonoflysineandmethioninecontentofproteinofvarioussources(Iqbal,1999)Furthermore, duckweed has been reported to be rich in vitamins containing around 40 differenttypes,notablyA,B1,B2,B6,C,E,andPP.Thetwolattervitaminsareparticularlyhighrangingfrom20ppmto60ppm(Iqbal,1999,p.56).

5.3MildlycontaminatedDuckweedIn the previous section human food and animal feed were discussed as products made fromduckweed.Whiletheseareinterestingoptionsforduckweedusage,theyrequirenon-contaminatedduckweedproducedinhumancontrolledsettings.Sincethisresearchfocussesonduckweedgrown

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in urban settings, waters are not always as pure and controlled as needed for food and feed(Fakhoorian, 2015; TenHaven, 2015). Yet this does not necessarily render the duckweed useless.Therefore, this section will focus on possible products of duckweed stemming from mildlycontaminatedwaterandduckweed.

5.3.1FertilizerThe lemnaaoukikusa and lemnaminor type of duckweed can be used as fertilizers (Suzuki et al.,2014). They are host to the cinetobacter calcoaceticus P23, a plant-growth promoting bacteria.ArtificialfertilizersareonlyavailabletoalimitedextendHence,naturalfertilizerscanhelpmeetingthedemand for fertilizers. Thesebacteriahave a growth stimulating effect onduckweed, yet it isunknown whether they affect other plants. Oron shows that duckweed cannot only be used asfertilizer, but argues that thewater it has purified can be used for irrigation of agricultural crops(1994,28-29).Figure5.2showstheinfluenceofduckweedinthenitrogencycle,whichisimportantasnitrogenenhancesplantgrowth.

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Figure5.2.Theroleofduckweedinthenitrogencycle(Oron,1994)Duckweed as fertilizer is practically unknown in the scientific community. As far as the literaturereview showed, hardly any research has been conducted regarding duckweed as a fertilizer. Yetsome practical applications have been found as Tamra Fakhoorian uses mildly contaminatedduckweedasfertilizer,andarguesthatthelevelofnitrogeninduckweedisimportantifonewantstouseitassuch.Basedonherexpertopinionitisbesttousetheduckweedinthegreenstateasitisless costlyand reduces theprocessing.However it canbeairdried to40-60%, the remaining40%wouldstillhavetobedried.Inthegreenstate,theduckweedhastobeusedasanoutsidefertilizeras inside it will mold. After the collection it can be spread out on the land. Depending on thenitrogen level, the farmer might need to add extra nitrogen. All in all, it is strongly advised toconductfurtherresearchinthisfield.

5.3.2SoilqualityenhancementDuckweed can be used to enhance soil quality through composting, and specifically throughvermicomposting,i.e.compostingconductedbyworms,withthehelpofEiseniafetidaearthworms(Kostecka & Kaniuczac, 2008). In Kostecka & Kaniuczac’s experiment compost pots of solelyduckweedandacombinationofduckweedandmanurewerecompared(2008).L.minorstemsfrommunicipal wastewater. As a result, the sole duckweed pots contained fewer worms, which areneededforefficientcomposting.However,thedifferencecouldbe influencedbytheexperimentalconditions(Ibid.).Theduckweedusedintheexperimentwasdry.Whengreenstateduckweedhadbeenused,thenitrogenandphosphoruslevelwashigherthancomposts.Moreover,Lotetal.(1979inIqbal,1999,p.61),Tai-hsinghetal.(1975inIqbal,1999,p.61)andWelwitsch(1859inIqbal,1999,p.61)foundthattheapplicationofduckweedonsoilsledtobettersoiltextureandbetterwaterandcation exchange, the soil capacity to exchange positive ions with the soil solution. Again, fewscientificarticlesonthissubjectexistandthereforepracticalexampleswillbeused.Thereisapatentstemming from 2002 of Kyle et al. on a technology to purify water with duckweed and use theduckweedtomakepulpthatenhancessoilquality.Aftertreatingthewastewater,theduckweediscollectedandturnedintopulpbymixingthegreenstateduckweedwithashreddedpaper(Kyleetal.,2002).Aftercreatingthepulp,itcanbeusedasabiodegradabledeliverypackage.whichcanlateronenhancethesoil.

5.4HighlycontaminatedDuckweedAsexplainedearlier,itispossibletousecontaminatedduckweedformaterialorenergyproduction.Ofcourse,theduckweeddoesnothavetobecontaminatedtobeusedforthepurposesthatwillbeintroducedbelow.Allduckweedissuitablefortransformationintheseproducts.

5.4.1Bio-energyThis firstpossibility for contaminatedduckweed is transformation intoenergy resources.Verma&Suntharhaveconstructedanoverview(figure5.3)ofvariousavailableformsofenergyresourcesandthe processes required for transformation (2015, p.5). The transformation process startswith theduckweedbiomass.SomestudiesindicatethatthelargertypesofduckweedsuchasS.punctate,L.gibba,L.minor,aremoresuitableforbiomassproduction(Xuetal.,2012,p.592).After duckweed collection there are threemain paths identified byVerma& Sunthar (2015, p.5):hydrothermalprocessing/upgradingandliquefaction,thermo-chemicalconversion,andbio-chemicalconversion,allofwhichwillbeexplainedinsomedetailbelow,andwillleadtodifferentoutcomes.Simultaneously,thedifferentprocessesdemanddifferentduckweed.Wetduckweedcanbeusedforhydrothermal processing, while dry duckweed is more suitable for thermo-chemical and bio-

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chemical conversion. Table 5.6 by Verma& Sunthar gives a first crude overview of the costs anddevelopmentstatusofthevarioustechniquesrequiredinthedifferenttransformationprocesses.

Figure5.3Possibilitiesforduckweedtoenergyconversion(Verma&Suthar,2015,p.5).Table5.6.Differentduckweedprocessesandapplicability(Verma&Suthar,2015,p.4).

HydrothermalconversionIn cases of wet duckweed, the aquatic plant can be used in hydrothermal processes where theduckweed is put in pressurized heated water. Depending on the pressure and temperature, it ispossibletoextractbiofuelsvialiquefaction,orbiogasviagasification(bothtechniquesareexplainedbelow in the thermochemical conversion discussion) (Tekin, Karagöz, & Bektaş, 2014, p.677).

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Unfortunately, Verma & Sunthar indicate that experience with these practices for duckweed arelimited(2015,p.4).ThermochemicalconversionDry duckweed can also be thermochemically processed, meaning that heat is used to turn theduckweed into fuels or gases. Dry duckweed can always be incinerated for heat. However, alsodifferentthermochemicalproceduressuchasgasification, liquefaction,orpyrolysisexistandmightbe more useful. Thermochemical gasification and liquefaction are used in a similar way forhydrothermal processes.When gasification is used (figure 5.9), theduckweed is heated to such ahigh level that either syn-gas or producer gas can be produced (Huber, Iborra, & Corma, 2006,p.4052). While producer gas is mostly used for electricity or heat, syn-gas is mainly used forprocessingintodifferentfuelsandproducts(Ibid.,p.4052).Figure5.4showsafewoftheseproductpossibilities. The gasification process can be enhanced by using solar powered gasificationtechniques, since it decreases the amount of burned biomass needed in order to reach the heatlevelsrequiredforthegasificationprocess(Ibid.,p.4055).Regarding liquefaction,astudybyXiuetal. argues that duckweed liquefaction can be used for bio-oil production (2010, p.1294-1297). Byconcentratingtheduckweedthroughashakerandbythenheatingitbetween260and340degreesCelsius for 60minutes the highest oil production results can be reached (Ibid., p.1294-1297). 340degreesseemstobethemaximumtemperatureformaximumoilyield,andusingacatalystreducestheoilyield.Xiuetal.analysisindicatedthattheoilyieldedfromthisprocesswasofgoodquality,ofaround33.95MJ/kg(withadeviationof1.79MJ/kg),andofbetterqualitythanoilproducedfrommanure or feedstock (Ibid., p.1298). Similarly, pyrolysis can be used. This process involves theheatingofduckweedwitha lackofoxygen,thuspreventing it fromcombusting,turning it intogasand/orbio-oil(Huber,Iborra,&Corma,2006,p.4052).

Figure5.4.Differentprocessestobio-energyidentifiedby(Huber,Iborra,&Corma,2006,4047).

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BiochemicalconversionThe thirdpath isbiochemical conversion (2015,p.5). Inbiochemical conversion,biochemistry (thestudy and use of the chemistry of biological processes) are used, is used to break down theduckweed to useable energy (Woods and Hall, 1994). When biochemical processes are used onduckweedforenergyproduction,someremarkshavetobemade.

Firstly,theusefulnessofduckweedforbioethanoldependsonthestarchcontentoftheduckweed.Themorestarch, themorebioethanolcanbeproduced.Variousstudies foundthis starchcontentvariedbetweenduckweedspeciesandcircumstancesfrom3to75%ofitsdryweight(DW)(Xuetal.,2012,p.591).Thestarch induckweed increaseswhen itsgrowthenvironment isnotoptimal (Ibid.p.591).Thus,duckweedcanbemanipulatedto increasestarch levels.Thiscanbeachievedby, forexample,depositingfreshlyharvestedduckweedintonutrient-poorwaterleadstonutrient-stressoftheduckweed,towhichtheduckweedrespondsbyproducingstarchtostoreglucose(Ibid.,p.595).Anothermethodmight be to use temperature differences because they are expected to increasestarch levels because lower temperature leads to a lower respiration level (Xu et al., 2011, p.70).Furthermore,itisalsopossibletoincreasestarchproductionbyincreasingthesalinityofthewater(Xuetal.,2012,598)orbyusingcertainchemicalssuchasabscisicacid,cytokinin,2-aminoindan-2-phosphonicacid(Ibid.595).Thestarchcanthenbetransformedintootherproductssuchasbioethanol.Thiscanbedonevia,forexample,hydrolysis functionssimilarly to thesaccharification (breakingcarbonmoleculesdowntosugars) of corn (Xu et al., 2012, 596) followed by fermentation. Cheng & Stomp showed, forexample, a fermentation process “using a-amylase (Sigma A3404), pullulanase (Sigma P2986) andamyloglucosidase(Sigma10115)”thattransformsthesugarintoethanol(Cheng&Stomp,2009,24).Another example is provided by Xu et al. who argue that it is also possible to use an enzymatichydrolysis (breaking down of molecules to sugars with enzymes), for example by using theMegazymeTotalStarchAssayProcedure(Megazyme,2014),“forduckweedsaccharification”(Xuetal., 2012, p.597). They then use “Saccharomyces cerevisiae (ATCC 24859) […] for ethanolfermentation”inordertotransformthesugarsintoethanol.(Xuetal.,2012,p.597).Xuetal.reportthatstudiesfoundthatthecreatedethanollevelstobearound96,2%(w/w)ofwhattheystatetobethetheoreticallymaximumamountofethanol(2012,p.597).Itisalsopossibletocreatebutanol.UsingacidichydrolysisandfermentationwithC.acetobutylicumCICC8012,forexample, leadstoahigher butanol production thanwhen using corn (Li et al., 2012, as found in Cui & Cheng, 2015,p.21).Another option using biochemistry can be found is reported by Cui & Cheng (2015, p.21). TheyreportthatstudiesofClark(1996),Triscarietal.(2009),andHuangetal.(2013)indicatewhensomeduckweedbiomassisaddedtotheinput,suchasmanure,foranaerobicdigesting,theproductionofbiogas increases substantially (Cui & Cheng, 2015, p.21). Thus duckweed could be used as anenhancing product as well. Concluding, there are many possibilities for the transformation ofbiomassintoenergyresources.

5.4.2BioplasticsAnadditionaloptionforthetransformationofduckweed intoproducts isbioplastics.Thisrequiresthat dry duckweed is processed in such away that its proteins and starch can be converted intopolymer (Zeller, Hunt, & Sharma, 2013, p.376-385).Because of the high starch content duckweedcouldpotentiallybeausefulproductforthebioplasticsindustry.AninfosheetbyBolch&Bosstatesthatusingextrusion,starchcanbeconvertedintothermoplasticstarch(THS)(2011,p.1).Thequalityof theTHScanbe improvedbyaddingadditionalmaterialssuchasplasticizers, to itscomposition,

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butthisisnotabsolutelynecessary(Bolck&Bos,2011,p.1).TheTHScanthanviavariousproductionmethodsbechangedintoaplasticend-product(Ibid.,p.1).

Zeller, Hunt, & Sharma argue in their research that duckweed can indeed be used as bioplastics(2013,p.381).Duckweedbioplastic“wascomparablewithotherbioplasticmaterials,andwithhighprotein raw duckweed material, or material which has been refined significant gains in materialproperties may be achieved” (Ibid., p.381). This means that duckweed has a large chance ofbecoming a useful bioplastic in the near future (Ibid., p.381). However, their experiment showedthat theduckweedwas lessuseful thanothermaterialsbecause their researchalso indicated thatthereisadifferenceinthepurityofthematerialbetweenduckweedgrownincontrolledwatersvis-à-visduckweedgrowninuncontrolledwaters(Ibid.,p.381-385).Someheavypollutantstakenupbyduckweed from public waters should not end up in the plastic, therefore it is important to filterthesepollutantsoutoftheduckweed.Howthatcanbeachieved,however,isoutsideofthescopeofthisresearch.

5.5SynthesisDuckweedcanbeturnedintomanyproducts.Theflow-chartbelow(Figure5.5.)sketchesthemainpossibilities this research found from the moment duckweed is collected to the end product.Depending on the level of contamination, it's dry or wet state, and the availability of processingmethods, different products can be created. It is always possible to use duckweed for waterpurification. Itneeds tobecollected inorder tobeeffective,otherwise thepollutantswill just re-enter the system. It is unlikely that human food can be produced from the urban waters in TheNetherlandsbecausethecontaminationlevelsarelikelytobetoohigh.Feedismorelikely,however,depending on the strictness of the legislation and the ability to remove pollutants from theduckweed.Duckweedasfertilizerorsoilenhancementhasnotbeenresearchedextensively,but isbelieved to be possible, both dry and wet. Additionally some research points in the direction ofduckweed as soil enhancer through composting. While it is slightly less effective as manurecomposting,duckweedprovidesanodorlessoption.However,morescientificresearchisneededonthesesubjects.Finallyitisalwayspossibletoturnduckweedintoenergyorplastics.Yet,thequalityoftheproductsisdeterminedbythemakeupoftheduckweed.Someproductshaveahigheraddedvalue than others. For example, turning duckweed into electricity is less valuable than using it toremovingpollutantsorphosphatesor turning it intohuman foodbecause theaddedvalueof thelatteroptionsarehighercomparedtotheaddedvalueofelectricity.Thechoicewhatkindofproductis chosen, is therefore not only a technical one, but also economical. The exact benefits of thesedifferentprocesseswillhavetobeanalyzedinanotherstudyinordertodeterminewhatthemostefficientoptionsforduckweedprocessingarefordifferentsituations.

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Figure5.5.Aflowchartoftheduckweedproductpossibilities

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6.TransitionmanagementandduckweedFollowing the transitionpathwaymethodologyofFoxonetal., in this sectionsub-question6,howthe niche market of duckweed can transition into the mainstream market, will be answered byperforming a market analysis, working from the macro to micro level, hence, starting withlandscape,followedbyregimeandniche(2010,p.1205-1208).

6.1Landscape

6.1.1LegislationMaessenstated that there isnocommon legislation regarding theuseofduckweed (2014,p,21).However, as this plant can be processed and used as a compound of different products, thelegislationthatappliestoeachspecificfieldofapplicationcanbediscussed.WaterpurifierUsingduckweedaswaterpurifierwouldhelptoattainthegoaloftheEuropeanNitrogenDirectivetoensureecologicalqualityofsurfacewaters(EU,1991)andtheEuropeanKaderrichtlijnwater(EUDirective2000/60/EG).Apossibleobstacleisthatduckweedcanonlybeusedinalimitedproportionastoomuchduckweedwillcausethedemiseofotherorganisms(WB21;Natura2000).Additionally,Nature 2000 sets rules formonocultures. In case of purification, duckweedwould be grown as amonocultureandthereforeNatura2000providesapracticallimitation.FoodandfeedDuckweed used for food and feed needs tomeet strict standards starting with the fact that theduckweedhastobeuncontaminated(Maessen,2014).Asthisresearchfocussesonurbanduckweedfromurbanwaters,whichisoftencontaminated,itwillbehardtousetheurbangatheredduckweedfor food and feed (Derksen& Zwart, 2010). An additional limitation is that it is considered as anagricultural product which also prohibits it use as human food (Rijksoverheid, 2013A). The onlypossibilitytoconvertduckweedintoanimalfeediswhenitisgrowninahighlycontrolledsettingasiscurrentlydoneonsustainablefarmsasECOFERM(VanWestreenen,2013).Therefore,thesetwoproductgroupsarenot considered in thismarketanalysis. If theseproductsare tobemade fromduckweed,thenitwouldbettertousecarefullycultivatedduckweedinclosedwatersystems.FertilizerandsoilenhancerAccordingtoMaessenduckweedfallsunderthecategoryof ‘remainingorganic fertilizer’,meaningtheduckweedcannototherwisebespecified(2014,p.22).Accordingly,somelimitationsapplytotheusage.Thistypeoffertilizercannotbeappliedtopasturesduringthegrazingseason.Whenthelandisusedforanimalfeedproduction,itcanonlybeuseduntilthreeweeksbeforetheharvest.Withinland employed for vegetable and fruit production (trees not included), this plant cannot be usedduring the growth phase of the fruit and on less than 10months before the harvest of fruit andvegetablesthatcomeintodirectcontactwithsoil.Further,duckweedasfertilizercannotbeused:-“whentheupperlevelofthesoilissaturatedwithwater;-fromSeptember1stuntilJanuary31stwhenthesoilisnotsimultaneouslyirrigated;-thereisaslopeof7%orhigher;-onarablelandwithaslopeof18%orhigher”(Maessen,2014,p.23).

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BioplasticsMost importantly regardingbioplastics is thepossibility of transfer of contaminants from thebio-plastic to the foodproductwhich ispacked (Rijksoverheid,2015A).Plasticderived frombiostarchhas a higher risk of contamination than conventional plastic stemming from oil. The currentchallenge will be meeting the standards for the packaging of food from the EU Directive1935/2004/EC and EU directive 10/2011/EC, substances that have influences on the food are notallowedtobeused(EUdirective10/2011/EC,p.22).Forotherproductstheregulationislessstrictasitdoesnotposeadirecteffectonthehumanhealth.Bio-energyTheDutchgovernmentpromotesatransitiontobiofuelsandthereforealotoflimitationshavebeenremovedin2013,makingthedevelopmentofbiofuelseasierasmoreorganicmaterialisallowedtobeused forproduction (Rijksoverheid, 2013B).However, it is not knownwhetherduckweed is anaccepted source, if not, this could limit duckweeds potential as biofuel in the Netherlands. Yet,currentlyduckweediscurrentlybeingusedinbiogasinstallations,indicatingtherearenomajorlegalobstaclesforusingduckweedassourceforbiofuel.Concluding, inregardstopreventionandcollectionmethodsonemustkeep inmindtheFloraandFauna legislation comprised in the EU biodiversity strategy of 2020 (Hagen, 2015). The collectionmight,infact,threatenfishpopulationsinthewaters,thisisconfirmedbyHoogheemraadschapDeStichtseRijnlanden(2014),andcould,thus,bealimitingfactor.

6.1.2ModeofgovernanceFollowingtheclassificationofDriessenetal.(2012,p.145-146),adecentralizedmodeofgovernancecan be identified. Duckweed is, indeed, removed by the water authorities, which is a form ofdecentralizedgovernmentalorganization,asmultiplewaterauthoritiesexist inTheNetherlandsonregional levels (Maessen, 2014, p.21). The duckweed removal is, thus, based on local publicgovernmentaldecision-making.Anadvantageofthistypeofgovernanceisthatthereishighchanceofstakeholderinvolvement.Thischaracteristicisresembledintheproblemathandas,accordingtoMaessen(2014,p.21),duckweed isonlyremovedafterreceivingcitizens’complaints.Hence, inputof citizens is taken seriously. Moreover, policy officer water Arthur Hagen, is initiating a projectregarding public participation concerning the duckweed removal. Yet so far, the mindsetsurroundingtheduckweed isratherpassive,andaccordingtoHagenprimarily focusedonremovaland preferably prevention (2015).Moreover themindset seems to be pessimistic as according toHoogheemraadschap De Stichtse Rijnlanden it is extremely costly and ineffective, indicating apreferenceforprevention(2014).

6.1.3SustainabledevelopmentFor the past few hundred years the promethean view of humans overcoming all problems bytechnological innovationhasbeendominantandwasrooted inmodernity thinking,capitalismandthe industrialrevolution(Hopwoodetal.,2015,p.38).Themainfocuswasoneconomicgrowthasbeing central tohumanwell-being. The growingenvironmental problemsand the social problemslinkedwith this gave rise to the concept of sustainable development, “meeting the needs of thepresentwithoutcompromisingtheabilityoffuturegenerationstomeettheirneeds”(WCED,1978inHopwoodetal.,2015,p.39).Thisreportpointedouttheimportanceofnatureforhumanwell-beingand since then sustainable development has become increasingly important for governments allovertheworld.TheNetherlandshastocomplywithEUenvironmentalpolicywhichhasdevelopedalongtermstrategyonsocial,economicandenvironmentalaspects(Eur-lex,NN).Thishasforcedthe

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Dutch government to broaden its mindset and to be open to innovative sustainable techniques.Therefore the government could be open to the application of duckweed to derive sustainableproducts.

6.2RegimeTheregimeidentifiedinthisresearchisthestatusquoofduckweed:duckweedaswaste.Currently,duckweedisremovedfromtheurbanwatersafterseveralcomplaintsafterwhichitisprocessedaswaste(Riemer,1994;Verma&Suthar,2015). Inthissectionthecurrentregimeisdescribedbasedonitsactivities.

6.2.1StakeholdersAccordingtoMaessenthewaterauthoritiesareinvolvedintheremovalofduckweed(2014).Theirapproachispassive:duckweedisonlyremovedaftercomplaintsfromcitizensorwhenitisblockingpumpingstations.Onewouldthinkthattoguardthewaterquality,duckweedwouldberemovedincasesofeutrophication.Citizens,areanothergroupofstakeholders.Urbancitizenssufferfromthestenchofduckweed.Astheunitofanalysisofthisresearchisurbanwater,onlytheurbancitizenswillbeaccountedforinthisresearch.Allinall,themunicipalityofTheHague,anotherstakeholder,gets around 12 complaints per year (Hagen, 2015).While it is themunicipality that receives thecomplaints, the duckweed removal is the responsibility of the water board. Yet the municipalitypreferstheduckweedgoneandmentionspreventionasthemostidealoption(Hagen,2015).CollectionThecurrentregimeofduckweedcollectionissimple.Duckweediscollectedbythewaterauthorities,or by firms contracted by thewater authorities, when there is a need to collect it.Maessen hasdeveloped a flow diagram (Figure 6.1) based on current duckweed removal practices that can beusedasabaselineforwhenduckweedisremovedandwhatstepsarebesttaken(Maessen,2014,p.31).Thebasicpracticeisthatwhentherearecitizencomplaints,actionistakenquicklytoremovethe duckweed and stop the complaints. If there aremore structural problems, for example withwaterquality,thenmorestructural(mainlyinfrastructural)approachesaretaken.Currently,thereisnoconformitywhatmethodistobeusedtoremoveduckweed.

Figure6.1.Aflowchartwhattodowithduckweed(Maessen,2014,p.31)

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WaterpurificationCurrently, two third of Dutch drinkingwater comes from groundwater (Water, 2008). Due to toomuchfertilizationinagriculture,chemicalsrunoff intothegroundwater.Yetthegroundwaterstillhasarelativelygoodquality,whichallowsforasimplefilteringtechniqueintheformofpumpingupthewaterandaddingoxygen.Thiscausethedirttolumptogetherandwillbefilteredoutbysand,gravelorcarbonfilters.TherestofthedrinkingwatercomesfromsurfacewaterstemmingfromtheRijnandtheMaas.Unfortunatelythedumpingofchemicalsharmsthewaterqualityinsuchawaythatitneedstobecleanedthoroughly.Thewatercanbepre-cleanedthroughfiltrationinthedunes,afterthisthesamepurificationasofgroundwatercanbeused.Thiscanbeseen indetail infigure6.2.Surfacewatercanalsodirectlybefiltered.Howeverthisismorecomplexasthewaterhastobedisinfected with chemicals, heating and filtering. Next to drink water purification there is thepurificationofwastewater,whichisdonebythewaterboards(Rioned,2009).Throughthesewagewater is transported to sewage water cleaning systems where the water is cleaned through thetechniquesdescribedabove.TheNetherlandsthusseemstohaveawell-organizedwatertreatmentsystem.

Figure6.2.Waterpurificationprocess(Kennislink,2010).FertilizercompaniesCurrently,theNetherlandsisalargeexporterofagriculturalproducts(NMI,NN,p.1)Itsclimateandfertile ground, togetherwithever increasing knowledge, technology andgoodorganizationof thewholesector,allowedtheagriculturalsectortoexpand.However,thedownsideofthisexpansionisincreasingpressureontheenvironmentduetoasimultaneousincreaseoffertilizersandpesticides.Itsconsequenceshaveledtoarefocusonsustainablefertilizers.Additionally,thesectorisstartingtorealize that the conventional fertilizers arenon-renewable and thereforeexhaustible.Next to thisone must keep the current policies in mind. Due to European legislation on nitrate and Dutchlegislationonwaterquality,theimportforfertilizersislimited.TheNetherlandsalsosuffersfromamanure fertilizer surplus and is obligated to minimize this surplus. Manure fertilizer would be acompetitionofduckweedandthereforelimitingduckweedpotentialtotransformfromanichetoaregime.Addingtothiscompetitionofanimalbasedfertilizersistheremovalofthemilkquota.Thisisexpected to lead to more animal feces. Hence, more competition for duckweed fertilizationpossibilities.However,inlinewiththebiobasedeconomy,thenutrientcycleisbeingreduced.Thiscouldbebeneficialtoduckweeds’possibilities,butitcouldalsopromotetheusageofanimalbasedfertilizer.After all, aswas shown in theproductanalysis,manurebased fertilizer ismoreefficientthanduckweedbasedfertilizer(Kostecka&Kaniuczac’s,2008).OneofthecurrentlybiggestfertilizerproducersisYarawhichsellsto150countriesincludingTheNetherlands.Yaraisalsoinfluencedbythe landscape of climate change and sustainable development and dedicated a CSR division tosustainable agriculture and fertilizers (Yara, 2012). Despite Yara’s good intentions, it assumes no

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change in the typeof fertilizer isneededwhen it is specificallyappliedwithnew techniques.Yarathereforedoesnotmentionthepossibilitiesofbio-fertilizers.WhenbigplayerslikeYara,whohavethe power to lobby in favor of conventional fertilizers, are not supporting duckweed additionalbarriers are created forduckweedmoving fromanichemarket to the regime (Kempet al., 1998,p.180).EnergycompaniesThe Netherlands has a centralized energy system based on large energy production plants and ahigh-voltage grid for electricity transportation and a country-wide network of gas pipes. It is aprivatized systemwhere the government facilitates and steers, but alsohas committed itself to atransition to sustainable sourcesofenergy.Themainpush towards sustainable formsofenergy isidentified in the Energieakkoord, an agreement the government concluded with companies andNGO’s in The Netherlands (Sociaal-Economische Raad, 2013, p.67-78). This Energieakkoord thusindicates the direction the government, companies and civil society are trying to push theNetherlands.Because the incumbentenergy regime is suchan importantpartof today’s societies(they are part of the infrastructure) it is difficult to actually reach radical changes in this system(Foxon, Hammond,& Pearson, 2010, p.1210; Kemp et al., 1998, p.177-179). There is, however, atendencyoftheregimetomovetowardswindandsolarenergy,whichithasalreadymadepartofits structure. However, the government does leave room for energy production from biomass.Currently,most biomass is used alongside fossil fuels in energy production. This biomass consistsmainlyofhouseholdwaste,wood,andmanure(EnergieonderzoekCentrumNederland,2015,p.62-64).Theprojectionsarealsonotveryhopefulfortherenewableenergysectorascanbeseeninfigure6.3,whichalsoshowsthatthestatusquoisreallyfossilfuelbasedandinvested.Whenlookingatalist(whichisincompletebecausealargecoalplantintheEemshaveninGroningenisnotonthelistyet)ofenergyplantsrecentlyconstructedintheNetherlands,itisclearthatmostinvestmentshavegoneintocoalandgasplants(Wikipedia,2015).Thusthereisastrongvestedinterestinkeepingcoaland gas in theNetherlands, because if these plantswere to be closed their ownerswould sufferlargelosses(Kempetal.,1998,p.179).

Figure6.3:PrimaryEnergyUseintheNetherlandspermajorenergyresourcegroup(EnergieonderzoekCentrumNederland,2015,p.78)

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PlasticproducersCurrently,mostplasticthatisbeingusedintheNetherlandsisoriginatedfromfossilfuels.However,it ispossible tomakeplasticoutofbiomass,suchasmays,sugarcaneandwood.Somebioplasticsarebiodegradable,somearenot.butthemarketisgrowingrapidly(EuropeanBioplastics,2014).Inthe Netherlands, multiple research institutes and companies are working on and producingbioplastics. In theprocess,biomass isbrokendown intosubstancessuchassugarorstarch,whicharethenprocessedintobioplastics.Someofthesecreatedbioplasticsarecombinedwithfossil-fuelplastics.Sofar,duckweedhasnotyetbeenusedtocreatebioplastics.Thebioplasticmarketisveryinnovative, and new ideas and pilots are constantly being created. In October 2015, the firstbioplasticwas created fromwastewater in theNetherlandswhile companies suchasAvantiumorBioHart,producebioplasticsbasedonbiomass(STOWA,2015).Concluding, it canbe argued that the regimeduckweed is facing ismainly a technological regime(Kempet al., 1998, p.182).Manydifferent techniques are in place that blockother techniques tomove into themainstreammarket.Notonlybecause theyareeconomically cheapandefficient incomparison with other techniques, but these techniques have also shaped contemporary society(Kempetal.,1998,p.178).For instance,energy techniques thatalloweda24hour reliableenergysupply, car travelling and flyinghavebecomenormal.Anewenergy source/ techniquemust thusalsoallowforthisreliability.Moreover,inTheNetherlandscitizensareusedtocleandrinkingwatereverywhere.Ifduckweedistoreplaceacurrenttechnique,ithastobecheaperandofferthesamestandards.

6.3NicheEventhoughthetransitiontoabiobasedeconomymightbeabouttoreachthekick-offphaseinthetransition cycle, duckweed is still in its pre-developmentphasewhere just somepilot studies andexperimentsarebeingconductedWaterpurificationThe manure surplus stemming from agriculture does not just provide a barrier in the form ofcompetition,butalsoanopportunityfortheuseofduckweedaswaterpurifier.Oneoftheproblemsofthemanuresurplusistherunoffintogroundandsurfacewaters,whichleadstolargeamountsofphosphorus and nitrogen accumulating in the waters (Rijksoverheid, 2015C). Both chemicals aredangerous tohumanhealthand should thereforebe limited.Asdescribed in theproduct analysispart, duckweed is capable to remove those chemicals from the water (Niewenhuis & Maring,2009,p.32). Thisprovides a viablepossibility forduckweed tomove fromaniche into the regime.However,currentpurificationmethodsfordrinkingwaterstemmingfromsurfacewateraresimpleandmight therefore not need duckweed (Water, 2008). Additionally, to convert surfacewater todrinkingwatermorecomplextechniquesareneededandduckweedisnotsufficientenough.Hence,the solid organized water treatment system in the Netherlands can be seen as a barrier to theapplicationofduckweedaswaterpurifier.Anotherobstacletotheuseofduckweedaswaterpurifieris that itcouldconflictwithWB21andNatura2000as it isamonocultureandtherebyathreattobiodiversity (Hagen, 2015). Yet it could play a role as pretreatment inwaterwayswere duckweednaturallygrows.Thiswouldreducetheintensityoflateroncleaning.

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FertilizersWhile there is a demand for organic fertilizer due to the depletion of chemical fertilizers, themainstreaming of duckweed as fertilizer suffers from some barriers as the competition with themoreefficientmanurebasedfertilizerandtheabolishingofthemilkquotaintheEU(NMI,NN).Yet,duckweedstillhasthepotentialtobecomeamainstreamfertilizer.AccordingtoDutchgovernmentmanure fertilizer can only be used to a limit as it is dangerous to human health (Rijksoverheid,2015B). The manure surplus thus only provides a limited competition to duckweed because themanuresurplusescannotbeusedasfertilizer.Whenthemanurefertilizerhasreacheditsallowablelimit, a shift to other organic waste is needed. This could become duckweed’s window ofopportunity.Additionallybecauseduckweedisodorless,thisbenefitcouldbeusedinmoredenselypopulatedareas.BiofuelsTheDutchnaturalgasproductionwilldeclinebothbecausethegasfieldsaregettingempty,butalsobecause of social factors such as the earthquakes in Groningen. The Netherlands will as aconsequence most likely import more gas from foreign partners (Energieonderzoek CentrumNederland, 2015, p.143-144). One of these is Russia, however, with ongoing tensions betweenRussia and the West, politicians have mentioned frequently that they do not desire to becomedependent Russian gas. Because duckweed can be turned into gas (or used to enhance gasproduction of anaerobic digestion processes), is available in the Netherlands, and fits to a largeextentinthecurrentinfrastructure,itcouldreducedependencyonRussiangasandreplacepartofthedwindlingnaturalgasproduction(Kempetal.,1998,p.177).Thesetypesofgasarecalledgreen-gas. It is expected that the Netherlands will develop towards this green-gas state, if the marketpricesdonotchangedramatically(EnergieonderzoekCentrumNederland,2015,p.132).Thisisevenmorelogicalwhenitisrealizedthatgreen-gasiscarbonneutralanddoesnotemitextragreenhousegassesintotheatmospherethanitabsorbedwhenthebiomasswasalive.Similarexpectationsexistfor bio-oil (ethanol) and bio-plastics (Energieonderzoek Centrum Nederland, 2015, p.8-79).Furthermore, to reach the climate goals in 2050, it is expected that a lot of biomass needs to beimportant for bioenergy purposes (Energieonderzoek Centrum Nederland, 2015, p.204-205). Ifduckweed were used, these imports could be reduced. Thus there are ample opportunities forduckweedfuels.However,oneofthemainobstaclesforbiomass-energyistheuncertaintythatenoughbiomasscanbe structurally and timely delivered to the power plants for a long period of time (Ibid., p.222).Moreover,duckweeddoesnotgrowwellinDutchwinterperiods.Therefore,itisdifficulttohaveastable flow of duckweed into the production system during winter. That is a barrier for its use,because either duckweedmust be stored as reserves to be used duringwinter, or other biomassproductsmustbeusedduringwinter.Anotherproblemisthattherehasbeenlittletonoexperiencewith(large-scale)fermentation,gasification,liquefaction,pyrolysis,orothermethods,ofduckweed,mainly because it turned out to be difficult to compete with fossil fuels and to develop goodbusinesscases(EnergieonderzoekCentrumNederland,2015,p.219-222).One practical example that is currently being undertaken in The Netherlands is that Rotie, acompany that collects organic waste and turns it into biogas or biofuel. They are going to testwhetherduckweedisapossibleorganicwasteproductthattheycanuseintheirproductionprocess(Rotie,2015).ThefirmIndaver indicatedthatduckweed indeedhaspotential tobeused,but italldependsonthecostsoftheduckweedinthegasproductionprocess(Indaver,2015).Unfortunately,in The Netherlands duckweed has not been tested on a large-scale yet. As a consequence, their

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benefitsandcostsarealsomoreuncertain,thustakingthesteptotrustthenewtechnologyismoredifficult(Kempetal.,1998,p.177-179).CollectionAsshowninchapter4anumberofcollectionmethodshavebeendevelopedbyvariousactorsthatarecapableofremovingduckweedfromwaterbodies.Someofthesefirmsarehiredtoremovetheduckweed,whileotherstrytoselltheirduckweedmachinestoactorsthatremoveduckweedsuchaswaterboardsoractorswithcontrolledduckweedbasins(Maessen,2014).However,whencollectingthe duckweed from public waterways, these collection practicesmust be able to collect just theduckweed and leave all other parts of the waterways alone. Unless, of course, the duckweedcollection machines can also at the same time collect and separate floating waste with theduckweed,becausethatwouldbeanaddedbonustothecollectionprocess.Shouldsuchacollectionmethod be developed, the added value for water boards will increase substantially. Themunicipalitiesareopenforinnovationwhichwouldallowanewcollectionmethodtotransformintoaregime(Hagen,2015).Thebiggestbarrierwillprobablybethebudgetasthecollectionmethodsdifferlargelyininitialcostsandmaintenancecosts(Maessen,2014).Rightnow,thenicheisstillquiteempty with few activities going on in public waterways. There are, however, possibly largeopportunities for duckweed collection bywater boards or private firms because of the increasingrecognition thatduckweedcanbeanvaluableorganism that canbe turned intoawide-varietyofproducts.Thatrecognitionwillincreasedemandforduckweed,whichrightnowisstillnon-existing,andthusincreasethepossibilitiestocollectanduseduckweedfrompublicwaterwaysbecausemoremoneywill become available to be allowed to use the duckweed, hence covering any associatedcoststhewaterboardmighthave.BioplasticsBecause plastic is made from, fossil fuels, there is a growing demand for bioplastics (EuropeanBioplastics,2014).However,sofar,biomassfromduckweedisstillresearchinprogress.Therearenoknowncompaniesorinstitutionsthatarecapableofturningduckweedeffectivelyandprofitablyintobioplastics. Especially the impurity of the duckweed from public waterways and the possiblepollutantsthatithastakenupcanbetroublesomewhenitistobeturnedintoduckweed,bothforhealth as for production reasons (Zeller, Hunt, & Sharma, 2013, 381-385). However, with thecontinuing interest and research into duckweed, it is possible that scientistswill findways to useduckweed effectively for bioplastics. Moreover, with the growing demand for bioplastics, thedemandfor itsresourceswill increaseaswell.Unlike importanttypesofbiomasssuchaswoodorcornandsugarcane,whicharealsodemandedforotherproductssuchasfood,buildings,furniture,andenergy,duckweedisstillaproductthatisopentoutilizationbyhumans.Thus,whiledemandforthecurrenttypesofbiomasswilllikelyincrease,alsobecauseofpopulationgrowth,duckweedisstillunexploited and can fill that gap. Therefore, duckweed has a lot of potential as a resource forbioplastics,butthatpotentialiscurrentlynotyetrealized.

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7.Discussion-ManagementadviceandTransitionpathwaysThe analysis carried out in the above chapters yielded several results regarding ecologicalinformation, prevention methods, collection techniques, products descriptions and marketpossibilities of duckweed in urbanwater systems in The Netherlands. Given these results severaldiscussion pointswill be discussed in order to provide an answer to the research question and amanagementadvice.Firstly, some general remarks regarding the research. The methodology mainly consisted of aliterature researchwhichwas complementedwith several interviewswith experts. Consequently,the report stays rather theoretical and is highly dependent on the quality of the studies used asreference.Additionally, the application to reality is not entirely known. Furthermore, due to timeconstraints,notallproductscouldbeconcludedintheanalysisandapre-selectionhadtobemade.Moretimewouldhaveallowedmore in-depthresearch.Nexttothis, the initialquestionposedbyKWRwas rather technical.While this is a transdisciplinary study, technical experts weremissing,leading to superficial technical analyses. If KWR indeed requires more insight in technologicalaspects, future research with technological experienced researchers is needed. One last generalremarkisthefocusontheNetherlandsingeneral.Duetopracticalinformationavailabilityandtimeconstraints, itwasnotpossibletofocusonaspecificDutcharea.Theconclusionscouldthusdifferforspecificareasandthereforetheresultsofthisresearchcannotbegeneralizedtootherareas.Secondly,asmentionedabove,duckweedcompositionishighlydependentonthecontaminationofthe water basin in which it grows. Water quality is a fundamental piece of knowledge to fullyunderstand the potential of duckweed and its possible application as a product. Giving the timeframeallowedforthisresearch,suchkindoftestingwasnotfeasible.Thus,futureresearchshouldaddressthespecificcompositionofduckweedspeciespresentinaparticularresearcharea.Thirdly,themostsuitablepreventionmethodisnotclearcutanddependsoncharacteristicsofthewaterway such as depth, nutrient concentration, flow velocity, dead ends, and its shape. Manyoptionshavebeenpresentedthatcanhelpreduceorpreventduckweedgrowthandshouldbetakenintoconsideration for implementation.However, future research isneeded todeterminehow theimplementation can be done most effectively and to highlight waterways for which preventionmightbethemostsuitableoption.Thisanalysisshouldconsiderelementsoftechnicalfeasibility,butalsointegratesocialnormsandacceptabilityconsiderations.Fourthly, regarding collection methods similar conclusions as for prevention techniques can bedrawn. Implementation of these practices depend on several parameters, namely duckweedcoverage, reachability, morphology, water depth and waterways surroundings. Thus, it isrecommended to research theseelements to assesswhichmethodsmightbemore successful forurban water basins. Further, we found that transport means have not yet been investigated indepth.Webelievethiselementshouldbecentraltothedeterminationofwhetherduckweedshouldbecollectedandprocessedorprevented.Thisisduetothefactthattrucksarethevehiclesmostlyusedfor transportandtheuseofsuchmeansmighthaveagreater impactonGHGemissionsandtheenvironmentratherthanpreventingthegrowthaltogether.Fifthly, thecurrentmodeofgovernancemighthinder the transitionofduckweedproducts fromanichetoaregimemarket.Todate, theonly institutions involved inthemanagementofduckweedareregionalwaterauthorities.Theinvolvementofotheractors,forexamplefromtheprivatesector,might enhance the chances of achieving the above mentioned transition and render the

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management of the duckweed resource more successfully. It is therefore suggested to take intoconsideration the possibility to embark on a partnershipwith the private sector. Particularly, twocompanies were found in the energy sector, Rotie and Indaver, who might be interested inprocessingtheduckweedrecoveredfromurbanwaterwaystoproducebiogas.Finally, for all possibilities presented in the above chapters, we suggest the client to undergo animpactassessmentandcostbenefitanalysis inordertodeterminenotonlythemosteconomicallyfeasible scenario, but also to understand the natural and social impact of specific methods.Considering thatDWA isapublicgovernmentalbodyand their final goalsdonot correspondwithincreasing their income, but providing a service to the community, and that KWR as a consultingbody should align with the objectives of DWA, we recommend that the latter two elements ofnatural and social impact assume a central role in the determination of the scenario to beimplemented.Figure7.1summarizespossiblescenariosthatmightresultfromprevention,collectionand processing of duckweed. Boxes in green indicate the recommended options based on urbanwatersystems.

Fig7.1.Flowdiagramwiththepossibilitiesofduckweed.LargerversioncanbefoundinAppendixI

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8.ConclusionThisresearchsetouttoanswerthefollowingresearchquestion:Inwhatway can prevention, collection, and processingmethods of duckweed in the urbanwatersystems of The Netherlands be managed to foster a transition from undesired waste to a usefulsustainableproduct?Afterprovidinggeneralbackgroundinformationontheecologyofduckweedprevention,collection,transportationmethodsandpossibleduckweedproductswereidentified.Thecontaminationlevelofthewaterandhencetheduckweedprovedtobeimportant.Ontheonehandviaeutrophicationitstimulatesduckweedgrowthandthusthenegativesideeffectsasstenchandhypoxia.Ontheotherhandthestimulationofduckweedgrowthopenspossibilitiesforduckweedbasedproductsofwhichthe level of contamination determines the possibilities. Another reason to keep contamination inmind,isthaturbanareas,suchastheDelflandarea,waterbodiesareoftencontaminated.Alogicalconclusionthereforewouldbetopreventduckweedgrowth,whichisthecurrentmunicipalpolicy.Loweringthenutrientlevelbydredgingwouldbethemostsuitableoptiontopreventduckweed.Yetasshowedabove,thereareseveralinterestingoptionstouseduckweed.Table4.4givesanoverviewofpossiblecollectionmethodsandwhenthesearemostsuitable.Manualtechniquescostlittleandscore relatively high in efficiency. However, on the long term the Proskim water skimmer andDuckweedguzzlerwouldbemoreprofitabledespitetheirhighinitialcosts.Thesemethodsaremoreefficient, cover a larger scale and facilitate transport. Flow-chart 7.1 shows the most promisingduckweedproducts(depictedingreen.)Duetostrictfoodsafetyregulations,foodandfeedoptionsarenotpossible.Mildlycontaminatedduckweedcouldbeusedasfertilizeroncethelimitformanureuseisreached.

Whileduckweedisslightlylesseffectiveasmanurecomposting,duckweeddoesprovideanodorlessoption.Finally,duckweedcanalwaysbeusedasingredientforbio-energyorbioplasticsasthelevelofcontaminationfortheseapplicationsisnotimportant.Hence,andcontaminatedduckweedcouldbeused.Bio-plasticsoffersanalternativetobio-plasticsfromsugarcanewhichcanbeusedforotherproduct.DuckweedBio-energy is thus themost interestingoption.However,duckweeds reliabilityas anenergy sourcemustbe tested.Additionally, turningduckweed intoenergyorplastics is lessvaluablethanturningit intohumanfoodforexample,astheenergyisburnedandlost.Therefore,thechoiceregardingthetypeofpotentialproductdoesnotonlydependontechnicalaspects,butoneconomicandsocialonesaswell.Moreover,duckweeddoesnotenter intoavacuummarket,buthastofindawayintotheexistingmarket.

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APPENDIXI:Flowchart

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APPENDIXII:Contactinformation

Typeoforganization OrganisationName Contactperson Contactinformation

Biogascompany Rotie MikeTiggeler mike.tiggeler@rotie.nl

Biogascompany Indaver RobertJansen Robert.Jansen@indaver.nl

Greenmaintenance HaegheGroup:duckweedcollectorsintheHague

RobertMolenkamp

RobertdenOude

DaphnevanGent

RobSnijders

R.Molenkamp@haeghegroep.nl,R.denOude@haeghegroep.nl,D.vanGent@haeghegroep.nl,R.Snijders@haeghegroep.nl

WaterGovernanceTheHaguemunicipality

TheHaguemunicipality

ArthurHagen arthur.hagen@denhaag.nl

Duckweedfarmer GreenSunProduc TamraFakhoorian tamraf9@gmail.com