Nitrification of vegetable waste using nitrifying
bacteria
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DOI: 10.1016/j.ecoleng.2017.07.003 CITATIONS0
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Ecological
Engineering
j o u r n a l h o m e p a g e :w w w . e l s e v i e r . c o m / l o c a t e / e c o l e n g
Nitrification
of
vegetable
waste
using
nitrifying
bacteria
Mitra
Naghdi
a,
Maximiliano
Cledon
a,b,
Satinder
Kaur
Brar
a,∗,
Antonio
Avalos
Ramirez
a,caINRS-ETE,UniversitéduQuébec,490,RuedelaCouronne,QuébecG1K9A9,Canada
bCentrodeInvestigaciónAplicadayTransferenciaTecnológicaenRecursosMarinosAlmiranteStorni(CIMAS),UniversidadnacionaldelComahue-Provde
RioNegro-CONICET,Guemes1030,8520SanAntonioOeste,RıoNegro,Argentina
cCentreNationalenÉlectrochimieetenTechnologiesEnvironnementales(CNETE),2263,av.duCollège,Shawinigan,QCG9N6V8,Canada
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:
Received3February2017
Receivedinrevisedform30June2017 Accepted3July2017 Availableonlinexxx Keyword: Nitrifyingbacteria Nitrite Nitrate
Organicfertilizersandvegetablewastes
a
b
s
t
r
a
c
t
Currentinorganicchemical-basedfertilizersforsoilshaveadverseimpactsonhumanhealthand envi-ronment.Inthepresentwork,twonitrifyingbacteria,i.e.Nitrosomonassp.DSM28437andNitrobactersp. DSM10236,wereexploredfortheproductionofnitrateinvegetablewastes.Forthispurpose,thenitrite productionbyNitrosomonassp.andnitrateproductionbyNitrobactersp.intwosyntheticmedia contain-ingammoniumandnitrite,respectivelywereinvestigated.Also,simultaneousgrowthofbothbacteria inasinglesyntheticmediumcontainingammoniumwasinvestigated.Finally,theperformanceofboth bacteriainamixtureofvegetablewastes,whereaconsortiaofmicroorganismspresentincattle-based compostproducedammonium,wereinvestigated.Highestconcentrationofnitrite(13.2ppm)andnitrate (1600ppm)inNitrosomonassp.andNitrobactersp.inoculatedsyntheticmediawereachievedafter12 and28days,respectively.Thesimultaneousgrowthofbothbacteriainsyntheticmediaandbothbacteria alongwithcompostmicroorganismsinvegetablewastesresultedin12and20ppmnitrate,respectively. Also,itwasobservedthatwithincreasingtime,theopticaldensityofNitrobactersp.populationincreased from0.04to0.72after35days,butforNitrosomonassp.,until12days,theopticaldensityincreased0.3 fromto0.6andthendecreasedto0.2onday21becauseofnitritetoxicitytothemicroorganism.The transformationofammoniumtonitrateusingNitrosomonassp.andNitrobactersp.insyntheticmedia andamixtureofvegetablewasteswasstudiedtodevelopaneworganicfertilizercontainingnitrogen source.
©2017ElsevierB.V.Allrightsreserved.
1. Introduction
Conventionalagriculturehasledtoanincreasingdependence onpesticidesandchemicalfertilizerstoaddressthefooddemands of theever-growinghumanpopulation(Santoset al.,2012; Tu etal.,2006).Pollutionofairand watermedia,suchas eutroph-ication of water bodies is caused by overuse of such chemical fertilizersenrichedwithknownquantitiesofnitrogen,phosphorus andpotassium,aswellasexcessivequantitiesofanimalmanure (Bhardwaj etal.,2014).Forexample, around13%–28% of nitro-genused for growingcrops is releasedto theatmosphere (Liu et al., 2014). Although chemical fertilizers may make a coun-try self-dependentin agricultural products, but it disturbsthe environmentwithitsharmfulimpactsonlivingorganisms. Fur-thermore,usingexcessamounts ofchemical fertilizersiscostly andcanleadtodepletionofwaterholdingcapacity ofsoilsand
∗ Correspondingauthor.
E-mailaddress:[email protected](S.K.Brar).
disparityinnutrients(Bhardwajetal.,2014;Raja2013;Youssef and Eissa 2014). Therefore, developing some affordable, effec-tiveandenvironmentally-benignfertilizershasbeenthefocusof researchers forlong time. Nowadays, somespecies of microor-ganismsarebroadlyusedduetotheirsignificantcontributionto providinganaturalsubstitutetochemicalfertilizers(Megalietal., 2014;Sahooetal.,2014).Encouragingorganicfarmingbyusing biofertilizersensuresfoodsafetyandimprovesthebiodiversityof soils(Araújoetal.,2008).
One ofthe mostimportant processesin natural fertilization processisnitrificationinwhichgaseousnitrogenistransformed intoammoniaandthentonitriteandfinallytonitratewhichis thepreferredformofnitrogenforplants.Thisprocessiscarried outthroughacomplex,sensitiveandslowsetofreactionsandthe involvedmicroorganismsrequirestrictaerobicconditions. There-fore,selectionofsuitablestrainsandprovidingrelatedconditions basedonthenatureofthesubstratearenecessary(Subbaraoetal., 2006,2009).
Nitrosomonas sp. and Nitrobacter sp. are important compo-nents of the soil microbial population that play major role in
http://dx.doi.org/10.1016/j.ecoleng.2017.07.003
2 M.Naghdietal./EcologicalEngineeringxxx(2017)xxx–xxx biologicalconversionof ammonia tonitriteand thentonitrate
(Nortonetal.,2002).Verhammeetal.,oxidizedammoniatonitrite bybothammoniaoxidizingarchaea(AOA)andammonia-oxidizing bacteria(AOB) byincubating soilsamples for28dayswith dif-ferentammoniumconcentrations(0–20gNH4+-Npergramof
soil).TheiranalysisshowedconsiderablegrowthofAOAatall con-centrations,whereas AOBgrowthwasimportantonly athigher concentration(Verhammeetal.,2011).GrunditzandDalhammar usedNitrosomonassp.andNitrobactersp.isolatedfromactivated sludge. The highest activity was reported tobe at pH 8.1 and 35◦CforNitrosomonassp.andpH7.9and38◦CforNitrobactersp. (GrunditzandDalhammar,2001).Blackburneetal.,investigated thecapabilityofNitrospirasp.andNitrobactersp.fortransformation ofnitritetonitrate.TheyfoundthatNitrospirahadlowerinhibition thresholdconcentrationsforfreenitrousacid(<0.03ppm)andfree ammonia(0.04–0.08ppm)comparedtoNitrobactersp.(Blackburne etal.,2007).
Agro-wastes,suchasmanures,hulls,leaves,plantstalksand vegetableresiduesareproducedfromdifferentagricultureandfood processingactivities,suchasdairyproduction,proteinextraction andbrewery.Theagro-wastes,suchasbreweryspentgrains,cheese processingresiduesandsoywasteareproducedinlargevolumes. Theyareoftenuselessforfarmersandcompaniesandtheywill oftenbediscardedrepresentingacostforproducers(LimandMatu 2015).Agro-wastescontainwatersolublecompoundse.g.,sugar andaminoacidsandinsolublecompoundse.g.,celluloseandlignin. Thesecompoundsarethemainnaturalsourceoforganicmatter insoil(Capraraetal.,2011).Therefore,duetotheirlowcost,no adverseenvironmentalimpactsbecauseoftheirbiodegradability andrichnessinwiderangeofnutrients,theagro-wasteshavea potentialtobeusedbyfarmerstoimprovethefertilityofsoil.
To thebest of our knowledge, there is no paper discussing theperformanceofnitrifyingbacteriainvegetablewastesamples. Inthis researchwork,theperformance ofNitrosomonas sp.and Nitrobactersp.intransformationofammoniumtonitriteandnitrite tonitratewereinvestigatedinsyntheticmediaandamixtureof vegetablewastes(acombinationofsoya,brewery,andwhey)in ordertodevelopaneworganicfertilizer.
2. Materialandmethods
2.1. Strainsandgrowthcondition
AnenrichedNitrosomonaseuropaea(DSM28437)and Nitrobac-ter vulgaris (DSM 10236) culture were obtained from Leibniz-Institut(DSMZ-DeutscheSammlung von).The compostedcattle manuremixedwithgardensoil(Nitrogen0.5%,Phosphate0.5%, Potash 0.5%)was purchased from Circle H Farms (USA). Nitro-somonas europaea was grown on 1583 medium for ammonia oxidizingbacteriathathadthefollowingcomposition:
Solution A: NH4Cl, 535mg; KH2PO4, 54mg; KCl, 74mg;
MgSO4×7H2O,49mg;CaCl2×2H2O,147mg;NaCl,584mg;Trace
elementsolution,1mL;Cresolredsolution,2mL;Distilledwater, 1000mL.
Trace element solution: Distilled water, 975mL; HCl, 1M 25mL; MnSO4×4H2O, 45mg; H3BO3, 49mg; ZnSO4×7H2O,
43mg; (NH4)6 Mo7O24×4H2O, 37mg; FeSO4×7H2O, 973mg;
CuSO4×5H2O,25mg.
Cresolredsolution:Cresolred,50mg;Distilledwater,100mL. ThepHwasadjustedto7.8byadditionof10%NaHCO3.
Nitrobactervulgariswasgrownon756Heterotrophicnitrobacter mediumthathadthefollowingcomposition:
SolutionA:2gNaNO2,Yeastextract,1.50g; Peptone,1.50g;
Na-pyruvate,0.55g;Traceelementsolution,1mL;Stocksolution, 100mL;Distilledwater,899mL.
Stocksolution:CaCO3,0.07g;NaCl,5g;MgSO4×7H2O,0.5g;
KH2PO4,1.5g;Distilledwater,1000mL;
Trace element solution: MnSO4×H2O, 33.8mg; H3BO3,
49.4mg; ZnSO4×7H2O, 43.1mg; (NH4)6Mo7O24, 37.1mg;
FeSO4×7H2O, 97.3mg; CuSO4×5H2O, 25mg; Distilled water,
1000mL.
ThepHwasadjustedto7.4withNaOHorKOH. 2.2. Growthinstandardmedia
TheculturemediawaspreparedasdescribedinSection2.1.Each strainwasrevivedtwotimesin150mLliquidstandardmediaat 28–30±1◦Cand150rpmfor3days.Also,compostwasinoculated intotwoculturemediatocomparewiththestrains. Theoptical density(OD600)andcolonyformingunits(CFU)permilliliterwere
measuredaftersecondrevivalforbothstrainsandcompostinthe twomedia.
2.3. Resistancetohighammoniaconcentration
Fiveflaskscontaining100mLofmedia1583withoutNH4Cland
withdifferentconcentrationofammoniai.e.100,250,500,750and 1000ppmwerepreparedandautoclavedat121±1◦Cfor20min. Later,theywereinoculatedwiththreemlofNitrosomonassp. inocu-lumandincubatedforsixdaysat37±1◦Cand175±1rpm.The concentrationofnitriteandammoniumweremeasuredafter6days andthetestsweredoneinduplicates.Thesetestswerecarriedout tofindmaximumconcentrationofammoniathatNitrosomonassp. cantolerate.
2.4. Kineticsstudyofnitrification
Media1583at150mLwithoptimizedconcentrationofNH4Cl
(obtainedfromSection2.3)waspreparedin250mLflasksand auto-clavedat121±1◦Cfor20minandthekineticsofgrowth,residual ammoniumandproduction ofnitritefor Nitrosomonassp.were studiedforthreeweeks.Similarly,150mLofmedia752was pre-paredin250mLflasks,autoclavedat121±1◦Cfor20minandthe kineticsofgrowthandproductionofnitrateforNitrobactersp.were studiedforfiveweeks.Also,kineticsofresidualammoniumand productionofnitriteinmedia1583inoculatedwithcompostand productionofnitrateinmedia756inoculatedwithcompostwere studiedforthreeandfiveweeks,respectively.
2.5. Vegetablewasteasgrowthsubstrate
In order to evaluate the potentialof vegetable waste tobe transformedintoausefulfertilizer,vegetablewasteswereused assubstratewithoutautoclaving.Thesubstratewascomposedof 36%soyawaste,54%brewerywasteand10%liquidwhey.Thetotal nitrogencontentofthesubstratewas2.98g/kg.Themediawere placedintwo2-Lflasksandtheirvolumeswereadjustedto1L usingmilli-Qwater.Oneflaskwasinoculatedwith10gcompost. Thesecondflaskwasinoculatedwith10gcompost,25mLof Nitro-somonassp.and25mLofNitrobactersp.Theprocedurewascarried outinduplicate.Duringfermentation,mediawereaerated.After1 week,thefinalconcentrationsofnitrateweremeasured.
2.6. Measurementofammonium,nitriteandnitrate concentrations
Tomeasure theammonium, nitriteand nitrate,colorimetric titrationwasemployed.Ammoniumwasdeterminedfollowingthe modifiedmethodofindophenolinwhichphenoliscombinedwith hypochloriteasit reactsinthepresenceof ammoniumtoform
Table1
Concentrationofammonium,opticaldensityandnitriteforNitrosomonassp. Parameter Unit Value
Initialammonium ppm 100 250 500 750 1000 Residualammonium ppm 80 240 480 740 980 Opticaldensity(660nm) – 0.362 0.072 0.056 0.008 0.002 Producednitrite ppm 0.3 0.1 0.1 0.1 0.1
indophenolblue.Thecolorintensityisproportionaltotheamount oftotalammoniumpresent.
Fornitrite,themethodofmodifieddiazotizationwasused.The samplereactedwith4-aminobenzensulfonicacidtoproduce vary-ingredshades.Thecolorintensitywasproportionaltotheamount of nitrite present. Similarly, nitrate concentrations were deter-minedbytransformingitbyusingareducingagent(NutrafinTM) toproduceacolorwiththeintensityproportionaltotheamount present.
3. Resultsanddiscussion
3.1. Resistancetoammonia
TheNitrosomonassp.wasgrownatsixlevelsofammonium con-centrationtoobserveitsnitrificationrate.Theconcentrationsof residualammoniumandproducednitriteagainstinitial concentra-tionofammoniumaregiveninTable1.Theresultsshowedhigher growth of Nitrosomonas sp. at lower ammoniumconcentration (100ppm) compared to intermediate or high levels of ammo-niumconcentration(250–1000ppm).Similarly,nitrificationrate washigheratlowerconcentrationofammonium.Itseemedthat freeammoniainhibitedtheactivityofNitrosomonassp.ata concen-trationhigherthan100ppm.Kimetal.,andYangetal.,observed similartrendsandreportedthathighfreeconcentrationof ammo-nia(NH3-N)inhibitedheterotrophic,nitriteoxidizingandammonia
oxidizingbacteria(Kimetal.,2006;Yangetal.,2004).Also, Vadi-veluet al.,observedthatfreeammonia upto16.0ppm,had no inhibitoryeffectoncatabolicoranabolicprocessesofthe Nitro-somonassp.(Vadivelu etal.,2006).Duetohighpermeabilityof freeammoniathroughcellmembrane,itwashypothesizedthat freeammoniamayaffectthecells bychanging intracellularpH, increasingenergyrequirements,orinhibittheirenzymatic reac-tions(GallertandWinter1997;Wittmannetal.,1995).
AccordingtoTable2,theinitialconcentrationofammonium wasadjustedto100ppmfortherestoftheexperiments.
Table2
NitriteandnitrateproductionusingNitrosomonassp.andNitrobactersp. Days NitriteProduction(ppm) NitrateProduction(ppm)
0 0.1 – 4 0.3 – 8 6.4 – 12 13.2 – 18 – 5 24 – 7 30 – 10 35 – 12
3.2. Nitriteandnitrateproduction
ThekineticsstudyofNitrosomonassp.andcompostinmedia 1583 and Nitrobacter sp.and compost in media756 were per-formed.Thetrendsofammoniumconsumptionandproductionof nitriteforbothcompostandNitrosomonassp.inmedia1583are shownin Fig.1AandB, respectively.AccordingtoFig.1A, con-centrationof nitritecontinuouslyincreasedupto8ppm within the test period in compost inoculated medium. However, for Nitrosomonassp.inoculatedmedium,amaximumnitrite concen-tration of 13.2ppm wasobserved after 12days. The maximum yieldofnitriteproductionafter12dayswascalculatedtobe0.9mg nitrite/mgammonium.Thereductioninproductionofnitritecanbe attributedtothetoxicityofnitriteforbacterialgrowth.Weonetal., observedsameinhibitoryeffectduringgrowthofAcinetobactersp. and theyreportedthatremoving nitritefromcultures reversed theinhibitoryeffect.Theyattributedthetoxicityofnitritetoits effectonbacterialmembranesandenergygeneration(Weonetal., 2002).AlsoitisreportedthatpHaffectsthistoxicitybyformation ofprotonatedspecieswithcapabilityofcrossingthemembrane (Anthonisenetal.,1976).
The variation of nitrate concentration within test period in media756inoculatedwithcompostandNitrobactersp.areshown inFig.2.Accordingtothisfigure,ittook35and28days respec-tivelyforcompostandNitrobactersp.inoculatedmediatoreach tothemaximum nitrateconcentrationof 1600ppm. The maxi-mumyieldofnitrateproductionafter28dayswascalculatedto be0.8mgnitrate/mg nitrite.Guo et al.,investigated the nitrifi-cation processin a10Lsequencingbatch reactorandobserved decreaseinammoniumandincreaseofnitriteandnitrate concen-trationsunderaerobiccondition.Finally,theyachieved25.7ppm nitrateand6.2ppmnitrite(Guoetal.,2009).Grigattietal., incu-bated soil,barkandmanurewithdifferentvolumeof activated sewage sludge for 72h. Theyfoundthat thenitrate
concentra-Fig.1.Concentrationofnitriteandammoniumatdifferenttimesfor:(A)compost;and(B)Nitrosomonassp.inmedia1583(Circleandsquarelegendsrepresentammonium consumptionandnitriteproduction,respectively).
4 M.Naghdietal./EcologicalEngineeringxxx(2017)xxx–xxx
Fig.2.Variationofnitrateconcentrationinmedia756inoculatedwith:(A)compost;and(B)Nitrobactersp.
tionincreasedwithincreasingamountsofaddedsewagesludge. Forsoil,barkandmanureincubatedwith10mLofsewagesludge, thetotal nitrateproduction was5073, 4801and 7530mgN/kg volatilesolids,respectively(Grigattietal.,2007).Accordingly,the obtainedresultfornitrateproductioninthisresearchwaswithin therangeobtainedbyotherresearchersthoughtheyuseddiverse microorganisms(presentinsewagesludge)insteadofusingsingle microorganism.
3.3. Growthrateofbacteria
The effect of time on the growth rate of Nitrosomonas sp. medium1583andNitrobactersp.inmedium756areillustratedin Fig.3.ForNitrosomonassp.(Fig.3A),amaximumbacterialdensity wasobtainedin12daysandsoonafter,thepopulationofbacteria decreasedsignificantly(p<0.03).ButforNitrobactersp.(Fig.3B), thebacterialpopulationreachedasaturationpointafter20days.
Thebacterial growth in batchsystem can bemodeled with fourdistinguishedphasesi.e.lagphase(A),exponentialphase(B), stationaryphase(C),anddeathphase(D).Inlagphase,cellsare adaptedtotheirnewenvironmentandinexponentialphase,the cellsmultiplyrapidly.Theexhaustionofnutrients(S≈0)and build-upofmetabolitesandwastematerialsleadtostationaryphasein whichthereisnonetgrowth.Indeathphase,thenumberofliving organismdecreases,duetotoxicmetabolitesandlackofnutrients
(Fargesetal.,2012).Forthisphase,thebalanceofcellmassina batchculturegives,byEqs.(1)and(2):
dX
dt =netX and X=X0(att=0) (1)
lnX
X0 =net(t−
t0) (2)
Wherenetisthemaximumspecificgrowthrate(1/time)andX0
andXarecellconcentrationattimet=0andt.Theparameternet
wascalculatedtobe0.1and1.1(1/day)forNitrosomonassp.and Nitrobactersp.,respectively.
3.4. Nitrificationinmedium1583withbothbacteria
According to Section 3.2, the maximum nitrite and nitrate productionwere13.2and1600ppminmedia1538and756, respec-tively.Thepossibilityofproductionofnitratewasinvestigatedin medium1583sothatafter12daysofinoculationofmedium1583 withNitrosomonassp.,Nitrobactersp.wasaddedtothemediumto convertnitritetonitrate.Theresultsofthisexperimentareshown inTable2.AccordingtothisTable,theconcentrationof nitrate reached12ppmafter35days.
For comparison, the nitrification test in medium 756 with Nitrobacter sp. was studied by setting the initialconcentration ofnitriteto13.2ppm anditwasobservedthatthenitrate con-centration reached16ppm after35days. Accordingly, theratio
Fig.3. Effectofstoragetimeonthegrowthof:(A)Nitrosomonassp.;and(B)Nitrobactersp.(Lagphase(A),logarithmicorexponentialphase(B),stationaryphase(C),and deathphase(D)).
Table3
comparativeperformanceofbacterialconsortiaintheproductionofsolublenitratestartingfromdifferentagroindustrialwastecombinations. Substratecomposition Strains Ammonium/
Nitrate(mg)
mgN/gsoil Reference Sorghumbagasse(88%)+pinebark(11%)+
Urea(1%)
Nitrobactersp.+Nitrosomonassp. 0.1 – Sánchez-Monederoetal.(2001)
Sorghumbagasse(86%)+pinebark(11%)+ brewerysludge(3%)
Nitrobactersp.+Nitrosomonassp. 0.4 – Sánchez-Monederoetal.(2001)
Ricestrawandcowdung(5:1:0.2) Geobacillus – 1.6 Sarkaretal.(2010)
Dairy-wastecompostorammoniumsulfate Geobacillus – 19.4 Sarkaretal.(2010)
Compost Unidentifiedconsortium 0.4 – Shietal.(2001)
Compost+ammoniumsulfate Unidentifiedconsortium 0.1 – Shietal.(2001)
Soybeanresidues+withleaves+sawdust (1:1:3)
Unidentifiedconsortium 25 – Josephetal.(2001)
Soyawaste+brewerywaste+whey (36%:54%:10%)
Nitrobactersp.+Nitrosomonassp. 0.35 20 Presentstudy Soyawaste+brewerywaste+whey
(36%:54%:10%))
Compost+Nitrobactersp.+Nitrosomonassp. 0.7 13 Presentstudy
ofnitriteconsumptiontonitrateproductionwas1.48mol/molN which is withintherange obtainedby otherresearchers. Trigo etal.,studiedoxidationofammoniuminasequencingbatch reac-torusingVandeGraafmedium.Theirresultsshowedthattheratio ofnitriteconsumedtonitrateproducedwas5.54mol/molN(Trigo etal.,2006).Inasimilarresearch,Fargesetal.,studiedthe per-formanceofNitrosomonaseuropaeaandNitrobacterwinogradskyi innitrificationandobserved thattheratioofnitriteproduction toammoniumconsumptionwas0.95mol/molNforNitrosomonas europaeaandtheratioofnitriteconsumptiontonitrate produc-tionwas0.975mol/molNforNitrobacterwinogradskyi(Fargesetal., 2012).Itseemed that thepresenceof Nitrosomonas sp.didnot interferetheconversionofnitritetonitratebyNitrobactersp. 3.5. Nitrificationinvegetablewaste
AsexplainedinSection2.5,thesyntheticmediawasreplacedby vegetablewastetostudythenitrificationperformanceofselected bacteria.Afteroneweek,thefinalconcentrationsofnitratewere 5ppmand20ppm(Fig.4)forsamplesinoculatedwithcompost andcompost/Nitrosomonassp./Nitrobactersp.,respectively.Atthis point, the process stopped due to simultaneous production of
Fig.4.ComparisonofNO3andSulfurproductioninppmbycommercialcompost
vscompost+Nitrobactersp.andNitrosomonassp.
solublesulfurouscompoundsthatreached11.8and30ppmineach medium,respectively.
AsshowninFig.4,thehigherthenitrateproduction,therewas higherthereleaseofsulfurfromtheselectedmediamixture.Inboth cases,thereleaseofsulfurwasslightlyhigherthanthenitrate.In thecaseofsoybean,itisreportedtohave5.7ppmofsulfur con-tent(Heetal.,2009)whilebrewerywastescontainsupto20ppm sulfate(Sudarjantoetal.,2011).Moreover,wheyisreportedto con-tainlargeamountofsulfur-containing aminoacids.Sincesulfur uptakebyplantsisapproximately0.25timesofnitrogen,itis rec-ommendedtoavoid wheyand maximizesoyawasteusein the mediainordertoobtainthebestnitratesulfurproportion. Accord-ingly,itisexpectedtoyieldupto60ppmnitrate.Thefinalsolution canbefurtherconcentratedtoincreasethenutrientsperliterto matchsyntheticfertilizers.However,furtherstudiesareneeded toachieveamaximumuptakebythetargetedplants,otherwise thenutrientswillendupintheenvironmentwhichcouldgenerate ecologicalproblemsforseveraldecadesasrecentlyreported(Meter etal.,2016).
FromTable3,itispossibletoseethattheadditionofcompost doesnotnecessarilyimplyanadvantage.Asseeninthetable,the highertheammonium/nitrate,thelessefficienttheresult.Sincethe usedmediawasnotsterilizedpriortouse,italreadycontained bac-teriathatwereabletocarryouttheammonificationstepneeded beforeNitrobactercanstartproducingnitrite.Moreover,the con-sortiumthatformscompostcontainsmanyotherlargebacterial populationsthancanleadtoundesiredresultslikethehighrelease ofsulfurcontainedintheamino-acidsofthemediathatleadsto nitrificationarrestduetotoxicity.Inthissense,itisvery impor-tanttoensurethatthesourceusedhasausefulproportionofN/S aswellastocontroltheparticipatingbacterialstrainsinorderto obtainaproperfinalconcentrationofnitratetobeusedasfertilizer andavoidingby-productsatthesametime.
4. Conclusion
Thetransformationofammoniumtonitriteandnitritetonitrate usingNitrosomonassp.andNitrobactersp.insyntheticmediaanda mixtureofvegetablewasteswasstudiedtodevelopaneworganic fertilizercontainingnitrogensource.Theresultsshowedthatthe highestconcentrationofnitrite(13.2ppm)andnitrate(1600ppm) insyntheticmediainoculatedwithNitrosomonassp.and Nitrobac-tersp.wereobtainedafter12and28days,respectively.Also,the presenceofbothbacteriainsyntheticmediaandbothbacteriawith compostmicroorganismsinvegetablewastesresultedin12and 20ppm nitrate,respectively.Therefore, vegetablewastescanbe consideredasapromisingcandidatefornitrogenrichbio-fertilizer.
Pleasecitethis article inpress as: Naghdi,M., etal., Nitrification ofvegetable wasteusingnitrifyingbacteria. Ecol.Eng.(2017), 6 M.Naghdietal./EcologicalEngineeringxxx(2017)xxx–xxx
Acknowledgments
TheauthorsaresincerelythankfultotheNaturalSciencesand EngineeringResearchCouncilofCanada(DiscoveryGrant355254) forfinancialsupport.Theviewsoropinionsexpressedinthisarticle arethoseoftheauthors.
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