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ColloidsandSurfacesB:Biointerfacesxx(2012)xxx–xxx
ContentslistsavailableatSciVerseScienceDirect
Colloids and Surfaces B: Biointerfaces
j our na l h o me p a g e :w w w . e l s e v i e r . c o m / l o c a t e / c o l s u r f b
Graphical Abstract
ColloidsandSurfacesB:Biointerfacesxx (2012)xxx–xxx Comparativestudyofthekineticsandequilibriumofphenolbiosorption
onimmobilizedwhite-rotfungusPhanerochaetechrysosporiumfromaqueoussolution ViktorFarkas,AttilaFelinger,AlˇzbetaHeged ˝usova,ImreDékány,TímeaPernyeszi∗
COLSUB53561
ARTICLE IN PRESS
G Model
ColloidsandSurfacesB:Biointerfacesxx(2012)xxx–xxx
ContentslistsavailableatSciVerseScienceDirect
Colloids and Surfaces B: Biointerfaces
j our na l h o me p a g e :w w w . e l s e v i e r . c o m / l o c a t e / c o l s u r f b
Highlights
ColloidsandSurfacesB:Biointerfacesxx (2012)xxx–xxx Comparativestudyofthekineticsandequilibriumofphenolbiosorption
onimmobilizedwhite-rotfungusPhanerochaetechrysosporiumfromaqueoussolution ViktorFarkas,AttilaFelinger,AlˇzbetaHeged ˝usova,ImreDékány,TímeaPernyeszi∗
Thebiosorptionprocessofphenolontofree,immobilizedwhite-rotfungiandalginatebeadswasexamined.Thebiosorptionprocess followspseudosecond-orderkineticsbyallbioadsorbents.Phenolbioadsorptionprocessfollowsananti-Langmuirbehaviorforfreefungal biomassandimmobilizedfungalbiomass.Thenonlinearestimationcanbesuggestedforbioadsorption-equilibriumevaluation.
Please cite this article in press as: V. Farkas, et al., Comparative study of the kinetics and equilibrium of phenol biosorption ColloidsandSurfacesB:Biointerfacesxxx (2012) xxx–xxx
ContentslistsavailableatSciVerseScienceDirect
Colloids and Surfaces B: Biointerfaces
j o ur na l ho me p a g e :w w w . e l s e v i e r . c o m / l o c a t e / c o l s u r f b
Comparative study of the kinetics and equilibrium of phenol biosorption on immobilized white-rot fungus Phanerochaete chrysosporium
from aqueous solution
1
2
3
Viktor Farkas
a,b, Attila Felinger
a,b, Alˇzbeta Heged ˝usova
c, Imre Dékány
d,e, Tímea Pernyeszi
a,b,∗4 Q1
aAnalyticalChemistryandGeoanalyticalResearchGroup,SzentágothaiResearchCenter,UniversityofPécs,H-7624Pécs,Ifjúságútja34.,Hungary 5
bDepartmentofAnalyticalandEnvironmentalChemistry,FacultyofScience,UniversityofPécs,H-7624Pécs,Ifjúságútja6.,Hungary 6
cDepartmentofVegetablesProduction,SlovakUniversityofAgricultureinNitra,SK-7624Nitra,Slovakia 7
dSupramolecularNanostructuredMaterialsResearchGroupoftheHungarianAcademyofSciences,UniversityofSzeged,AradiVértanúktere1.,H-6720Szeged,Hungary 8
eDepartmentofMedicalChemistry,FacultyofMedicine,UniversityofSzeged,AradiVértanúktere1.,H-6720Szeged,Hungary 9
10
a r t i c l e i n f o
11 12
Articlehistory:
13
Received4June2012 14
Receivedinrevisedform1September2012 15
Accepted6September2012 16
Available online xxx 17
Keywords:
18
Biosorption 19
Phenol 20
Ph.chrysosporium 21
Kinetics 22
Equilibrium 23
Nonlinearleast-squaresestimation 24
a b s t r a c t
Inthisstudythekineticsandequilibriumofphenolbiosorptionwerestudiedfromaqueoussolutionusing batchtechniqueataninitialpHof5.5.ThebiosorptionwasstudiedonCa–alginatebeads,onnon-living mycelialpelletsofPhanerochaetechrysosporiumimmobilizedonCa–alginate,andonfreefungalbiomass.
Ph.chrysosporiumwasgrowninaliquidmediumcontainingmineralandvitaminmaterialswithcomplex composition.Thebiosorptionprocessfollowedpseudosecond-orderkineticsonallbioadsorbents.The bioadsorption-equilibriumonblankCa–alginate,freeandimmobilizedfungalbiomasscanbedescribed byLangmuir,anti-LangmuirandFreundlichisothermmodelsusingnonlinearleast-squaresestimation.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
25
Phenoliswidelypresentinwastewatersdischargedfromindus-
26
triesanditisconsideredasprioritypollutantbecauseofitshigh
27
toxicityatlowconcentrationsaswell.Industrialsourcesofcontam-
28
inantssuchasoilrefineries,coalgasificationsites,petrochemical
29
units,and so on, generate largequantitiesof phenols. In addi-
30
tion,phenolderivativesarewidelyusedasintermediatesinthe
31
synthesis of plastics, colors, pesticides, insecticides, etc. [1]. In
32
ordertokeepwatersfreefromphenolcompounds,differentpurifi-
33
cation methodssuchas adsorption,chemical oxidation,solvent
34
extraction,orreverseosmosisareusedforremovingphenolsfrom
35
wastewaters[2].
36
Biosorption, as an efficient, cost-effective and environmen-
37
tallyfriendly technique– forheavy metals andvarious organic
38
pollutants– hasemerged asa potentialalternativetothe con-
39
ventional techniques [3–6]. Biomass of somenatural microbial
40
species,includingbacteria,fungiandalgae,iscapableofremoving
41
∗Correspondingauthorat:H-7624Pécs,Ifjúságútja6.,Hungary.
Tel.:+3672503600;fax:+3672501518.
E-mailaddress:ptimea@gamma.ttk.pte.hu(T.Pernyeszi).
thedifferentorganicpollutantsbybiosorption,biodegradationor 42
mineralization[7,8]. 43
Growingattentionisbeinggiventothepotentialhealthhaz- 44
ardpresentedbyheavymetalstotheenvironment.Uluozluetal. 45
used lichen biomass for theremoval of different heavy metals 46
fromaqueoussolution.Theystudiedtheeffectofdifferentparam- 47
eters,suchaspH,biomassdosage,contacttime,andtemperature. 48
[9].Biosorption ofCd(II) andCr(III)fromaqueoussolutionon 49
Hylocomium splendens biomass wereinvestigated by Sari et al. 50
Theyuseddifferentkineticandisothermmodelstoevaluatethe 51
experimentaldata.TheyfoundthattheLangmuirmodelfittedthe 52
equilibrium databetterthantheFreundlichone.Theuseofthe 53
Dubinin–Rhadushkevichmodeldemonstratedthattheprocessis 54
ion-exchange[10].Lactofungusscrobiculatusbiomasswasusedfor 55
heavymetalremovalbyAnayurtetal.Thekineticstudiesindicated 56
thattheprocessfollowedwellpseudosecond-ordermodel.The 57
recoveryofthemetalionwasfoundashigherthan95%[11]. 58
Phanerochaetechrysosporiumisawell-knownwhite-rotfungus 59
andithasastrongabilitytodegradexenobiotics[12,13].Relatively 60
fewstudieshavebeencarriedoutwithPh.chrysosporiumindetox- 61
ifyingmetaleffluentsandeffluentscontainingphenolderivatives 62
[6,7,14–19].Moststudiesonbioadsorptionwerecarriedoutwith 63
powderedbiomassandbatchsystems.Thepowderedbiomassis 64 0927-7765/$–seefrontmatter© 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.colsurfb.2012.09.029
Please cite this article in press as: V. Farkas, et al., Comparative study of the kinetics and equilibrium of phenol biosorption on immobilized white-rot fungus Phanerochaete chrysosporium from aqueous solution, Colloids Surf. B: Biointerfaces (2012), http://dx.doi.org/10.1016/j.colsurfb.2012.09.029
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2 V.Farkasetal./ColloidsandSurfacesB:Biointerfacesxxx (2012) xxx–xxx difficulttouseinapplicationsduetoitsdisadvantages,thesmall
65
particlesizeandlowmechanicalstrength,whichmaycausediffi-
66
cultyintheseparationofbiomassafterbiosorptionandsignificant
67
masslossafterregeneration.
68
Theimmobilizationofnativemicroorganismsonnaturalorsyn-
69
theticpolymersimprovestheirmechanicalstrength,rigidity,size,
70
porositycharacteristics,andresistancetoenvironmentalrestrains.
71
Theselectionofimmobilizationmatrix iscrucialintheapplica-
72
tionofimmobilizationbiomass.Thepolymermatrixdetermines
73
themechanical strength,rigidity,and porositycharacteristicsof
74
theimmobilizedbeadsandtheiradsorptioncapacity.Thephysi-
75
calentrapmentofmicroorganismsinsideapolymermatrixisone
76
ofthemostwidelyused techniquesorimmobilization[20–27].
77
Sodium alginate, chitin, chitosan, and cellulose derivatives as
78
naturalpolymershavebeenusedasthematricesforimmobiliza-
79
tion[20–27].Immobilizedbiomassexhibitsagreaterpotentialin
80
fixed/fluidizedbed reactors becauseof minimal clogging under
81
continuousflowingconditions,convenienceforregeneration,reuse
82
ofbiomassandeasysolid–liquidseparation[3,26,27].
83
For the immobilization of Ph. chrysosporium, little informa-
84
tionexistsintheliterature.YuandWu[25]usedalginate,pectin
85
and polyvinyl alcohol (PVA) to immobilize Ph. chrysosporium
86
cellsfor2,4-dichlorophenolbioadsorption.Theimmobilizationof
87
Ph.chrysosporiumonto pectin wasless efficient than that onto
88
othermatrices becauseofitspoormechanicalstrengthand low
89
adsorptionefficiency.Ca-alginateimmobilizedfungalbeadswith
90
biocompatibilityexhibitedgoodmechanicalstrengthandadsorp-
91
tionefficiencyover60%.Amongthedifferentbiomassdosagein
92
Ca–alginateimmobilizedfungalbeads1.25%(w/v)wastheopti-
93
mum[20,25].
94
The continuous-flow adsorption of 2,4-dichlorophenol (2,4-
95
DCP) from aqueous solutionon immobilized Ph.chrysosporium
96
biomass in a fixed-bed column was also studied [26]. They
97
foundthatthebreakthroughtimedecreasedwithincreasingflow
98
rate,increasinginfluentconcentration,anddecreasingbeddepth.
99
Thedata alsoindicated thatthe equilibrium uptakeof 2,4-DCP
100
increasedwithdecreasingflowrateandincreasinginfluentcon-
101
centrationof2,4-DCP.
102
MathialaganandViraraghavanstudiedthebiosorptionofpen-
103
tachlorophenol(PCP) ontreatedAspergillus niger biomass.They
104
foundthatthebiosorptionwaspHdependent.TheremovalofPCP
105
decreasedwiththeincreaseofpHforalltypesofbiomass.Theyalso
106
evaluatedtheresultswithdifferentkineticandisothermmodels
107
[8,28].
108
Ca–alginateandloofaspongeasasupportforlead(II),copper
109
(II),andzinc(II)biosorptiononimmobilizedPh.chrysosporiumwas
110
alsostudied[20,21,23].IqbalandSaeedreportedthepossibilityof
111
immobilizingPh.chrysosporiumonabiostructuralmatrixofloofa
112
spongeasadyebiosorbentsystemfortheremovalofRBBR(Rema-
113
zolBrilliantBlueR), areactivedye,fromaqueoussolution.The
114
reactivedyeuptakefromaqueoussolutionwasfoundtobeinflu-
115
encedbysolutionpH,temperatureandinitialdyeconcentration
116
[23].
117
ThefibrousnetworkofPapayawoodasaspecialimmobiliza-
118
tionmatrixwasusedtoimmobilizePh.chrysosporiumbyIqbaland
119
Saeed[22].Theyusedthismatrixforremovalofzinc(II)fromaque-
120
oussolution.Theyobtainedthattheimmobilizedfungalbiosorbent
121
removedzinc(II)rapidlyandefficientlywithamaximummetal
122
removalcapacity of 66.17mgg−1 at equilibrium, 41.93% higher
123
thantheamountofzinc(II)removedbyfreebiomass.Thesorp-
124
tiondataagreedwellwiththesecond-order kineticmodel,the
125
equilibriumdatafittedverywelltotheLangmuirmodel.
126
Themain objective of thepresent study wasto immobilize
127
inactive Ph. chrysosporium fungal biomass in Ca–alginate poly-
128
mermatrix andevaluatethephenolbioadsorptionkineticsand
129
equilibriumonblankCa–alginate,immobilizedPh.chrysosporium
130
fungalbiomasswithcomparisonoftheadsorptiondataonfreePh. 131 chrysosporiumbiomass,TheeffectofpH,adsorptiontime,initial 132
phenolconcentrationonbioadsorptioncapacitywasstudiedina 133
batchsystem. 134
2. Experimental 135
2.1. Chemicals 136
Allchemicalsusedwereofanalyticalgrade.Na–alginatewas 137
purchasedfromSigmaAldrichLtd.,Germany.Phenol(>99%purity) 138
waspurchasedfromSigma–AldrichLtd.,Germanyandwasused 139
withoutfurtherpurification.Stocksolutionswerepreparedbydis- 140
solving0.2gofphenolin1.0Lofdistilledwater.Thetestsolutions 141
containingphenolwerepreparedbydiluting200mgL−1ofstock 142
solutionofphenoltothedesiredconcentrations.ThepHvalueofthe 143
biosorptionsystems(2.0–7.0)wasadjustedtotherequiredvalue 144
using0.1MNaOHor0.1MHCl(MerckAG.,Germany)solutions.All 145
solutionswerestoredinthedarkat4◦Cpriortouse. 146
2.2. Cultivationoffungalbiomass 147
Ph.chrysosporium(strainSzMC1726)obtainedfromtheDepart- 148
mentofEnvironmentalMicrobiology,FacultyofScience,University 149
ofPécs(Hungary)wasusedinthisstudy.Itwascultivatedasprevi- 150
ouslydescribedbyKirketal.[29].After5daysincubationat35◦C 151
onashaker(app.180rpm),themycelialpelletswereremovedfrom 152
themediumthroughfiltrationandinactivatedinapressurecooker 153
athightemperature(120◦C)for20min.Thenthemyceliapellets 154
werewashedseveraltimeswithdeionizedwater.Thesemycelial 155
pelletswereimmobilizedinthenextstep. 156
2.3. ImmobilizationofPhanerochaetechrysosporiumin 157
Ca–alginatebeads 158
Forimmobilizationoffungalbiomass,theoptimumconcentra- 159
tionofPh.chrysosporiumbiomassandNa–alginatesolutionwas 160
determinedbyWu andYu[25].Theoptimized concentrationof 161
biomassinCa–alginatewas1.25%andtheoptimizedconcentra- 162
tion ofNa–alginate solutionwas2%. For the immobilizationof 163
biomass,these concentrationvalues wereused.Fungal suspen- 164
sionwasdroppedinto a0.2MCaCl2 solution,andthedropsof 165
alginate–biomassmixturewerelatergelledintobeadswithamean 166
diameterof3–4mm.TheCa-alginateimmobilizedPh.chrysospo- 167 riumbeadswerestoredintheCaCl2solutionatfridgetemperature 168
around5◦C for4htocure.Thenthebeads wererinsedseveral 169
timeswithdeionizedwaterandstoredinfridgepriortouse.For 170
blankCa–alginatebeads,similarprocedureswereusedbutwithout 171
fungalbiomass. 172
2.4. Biosorptionstudy 173
ThebiosorptionofphenolontotheblankCa–alginatebeads,free 174
andimmobilizedfungalbeadswasinvestigatedinbatchbiosorp- 175
tionsystems. 176
Forcomparison,0.075goffreebiomass(dryweight),immo- 177
bilizedfungalbeadscontaining0.075gbiomass(dryweight)and 178
blankbeads(dryweight) wererespectively mixedwith250mL 179
phenolsolutionat theconcentrations of25 and 50mgL−1.The 180
sampleholderwasagitatedonashakerat400rpmatroomtem- 181
perature.Samplesweretaken atgiven timeintervals,and then 182
centrifugedat10,000rpmfor5min.Thesupernatantwasusedfor 183
analysis. 184
Forequilibriumstudies,theblankbeads,thefreeandimmobi- 185
lizedfungalbiomasswererespectivelyputintophenolsolutions 186
Please cite this article in press as: V. Farkas, et al., Comparative study of the kinetics and equilibrium of phenol biosorption V.Farkasetal./ColloidsandSurfacesB:Biointerfacesxxx (2012) xxx–xxx 3
Fig.1.Stereomicroscopicview(a)ofCa–alginatebead,freebiomass,andimmobilizedbiomass.Scanningelectronmicroscopicimageof(b)theCa–alginatebead(at70×
magnification),(c)ofthesurfaceoftheCa–alginatebead(at1000×magnification)and(d)ofthehyphalstructureoffreePh.chrysosporiumbiomass.Diametersofthebeads areabout5mm.
withinitialconcentrations from 10 to100mgL−1. Theconcen-
187
trationof biosorbentwas0.3gL−1,thesuspension volumewas
188
50mL.Theexperimentswerecarriedoutat22.5◦Ctemperature.
189
Theadsorbedamountofphenolwascalculatedwiththefollowing
190
equation:
191
q=(C0−Ce)V
m (1)
192
whereqistheadsorbedamountofphenol(mgg−1);C0istheinitial
193
phenolconcentration(mgL−1);Ce istheequilibriumphenolcon-
194
centration(mgL−1);Visthevolumeofthesolution(L);andmis
195
theweightofthebiosorbent(g).
196
2.5. Analysis
197
HPLC(AgilentTechnologies,USA)wasusedtodeterminethe
198
equilibriumconcentrationofphenolinthesupernatant.TheHPLC
199
systemcontainedadegasser(Agilent1100Series),asystemcon-
200
troller(Agilent1200Series),anautosamplerandinjector(Agilent
201
1200Series).TheChemstationsoftwarewasusedtoevaluatethe
202
chromatographicdata.Theexperimentswereperformedwitha
203
UV/visphotodiodearraydetectoratthewavelengthsof217and
204
270nm.
205
AWatersSymmetryC18column(4.6mm×150mm;5mpar-
206
ticlesize) was used. Allthe measurement werecarried out in
207
isocraticmodeusingthemobilephasecomposition60:40%(v/v),
208
methanol:water).Theseparationconditionswerethefollowing:
209
flowrate1mLmin−1,columntemperature50◦C,andinjectionvol-
210
ume20Lforboththestandardandsamplesaswell.Calibration
211
curveofthestandardwasmadefromstocksolutionintherangeof
212
10–100mgL−1.
213
2.6. Morphologicalstudywithscanningelectronmicroscope 214
(SEM) 215
SEMstudieswereconductedintheCentralElectronMicroscope 216
Laboratory,FacultyofMedicine,UniversityofPécs.AJeolJSM-6300 217
(JeolLtd.,Japan)scanningelectronmicroscopewasusedinthis 218
study. 219
Sampleswerelyophilizedasadryingprocedure.Nofurtherfixa- 220
tionproceduresweredoneduringthesamplepreparationprotocol. 221
Beforethesampleshadbeencoveredwithgold,dehydratedgran- 222
uleswerefixedonamicroscopeslide(Fig.1). Q2 223
3. Resultsanddiscussion 224
3.1. TheeffectofinitialpHonphenolbioadsorptionon 225
Ca–alginate,immobilizedandfreePh.chrysosporiumbiomass 226
EarlierstudiesonbiosorptionhaveshownthatpHisanimpor- 227
tantparameteraffectingthebiosorptionprocess[30].Theeffect 228
ofthepHoftheinitialsolutiononthephenoluptakecapacityof 229
theadsorbents(Ca–alginateblankbeads,Ca–alginateimmobilized 230
Ph.chrysosporiumbiomass,and free Ph.chrysosporiumbiomass) 231
wasstudiedinthepHrange2.0–7.0atasuspensionconcentration 232
of0.3gL−1.OnecanseeinFig.2a–cthatthebiosorptionofphe- 233
nolfirstincreasesfrompH2.0andthendeclineswiththefurther 234
increaseofpH.ForCa–alginatebeads,themaximumequilibrium 235
phenoluptake wasfoundat 1.21and2.22mgg−1,respectively, 236
for25 and50mgL−1 atpH6(Fig.2a)Foralginateimmobilized 237
fungalbiomass,themaximum equilibriumuptakewasfoundat 238
2.06 and 3.93mgg−1, respectively, for 25 and 50mgL−1 phe- 239
nol concentrations atpH6 (Fig. 2b).For free Ph.chrysosporium 240
biomass, the maximum equilibrium uptake was foundat 2.82 241
and5.25mgg−1,respectively,forphenolconcentrationsof25and 242
Please cite this article in press as: V. Farkas, et al., Comparative study of the kinetics and equilibrium of phenol biosorption on immobilized white-rot fungus Phanerochaete chrysosporium from aqueous solution, Colloids Surf. B: Biointerfaces (2012), http://dx.doi.org/10.1016/j.colsurfb.2012.09.029
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Fig.2.TheeffectofpHonphenolbiosorptionprocessby(a)Ca–alginate,(b)immobi- lizedPh.chrysosporiumbiomassand(c)freebiomassatinitialphenolconcentrations of25and50mgL−1inaqueoussuspension.Thebiomassconcentrationis0.3gL−1. Errorbarrepresentsstandarddeviation(SD);n=3.
50mgL−1(Fig.2c).DuringtheadsorptionprocesstheadjustedpH
243
valueofthesuspensionsdidnotsignificantlyvaried.
244
Similar trends were observed for two initial concentrations
245
in the case of Ca–alginate, immobilized and free biomass.
246
Withincreasinginitialconcentration,thephenoluptakecapacity
247
increasedinallcases.Inthecaseoffreebiomassandimmobilized
248
biomass,inthenaturalstateofpH5.0–6.0,theadsorptionofphenol
249
wasatthemaximumlevel.InthecaseofCa–alginateimmobilized
250
biomass,theadsorptionwasatmaximumatpH6.0.Thebioadsorp-
251
tionwasslightlyreducedinalkalineandacidicmedium.Theeffect
252
ofpHonphenolbioadsorptionwasnotsignificantinthepHrangeof
253
6.0–8.0,andtheuptakeofphenolinthatpHrangewaslargerthan
254
atotherpHvalues.ThepHofthesolutioninfluencesboththecell
255
surfacebindingsitesandchemistryinwater.Earlierstudiesfound 256
thattheadsorbedamountcorrelated withthedissociation con- 257
stantofphenolderivatives[7,15,19].Theionicfractionofphenolate 258
ionincreaseswithincreasingpHandthesurfacechargeoffungal 259
biomassispredominantlynegativeatpH3.0–10.0[7,15,19,31].It 260
wasalsoreportedthattheelectrostaticforcesbetweenthecharged 261
fungalsurfaceandphenolplayedanimportantroleinthebioad- 262
sorptionprocess. 263
Inourearlierstudy,theinfluenceofpHonphenolbioadsorp- 264
tionwasalsoinvestigatedonfreedeadPh.chrysosporiumbiomass, 265
buttheculturalmediumhadadifferentcompositionwithasimple 266
constitution.ThemaximaluptakecapacitywasobtainedatpH5.5. 267
Inthepresentstudy,theculturalmediumforfungalbiomasshasa 268
complexcomposition[32].WuandYu[25,33]foundthatthemax- 269
imumuptakecapacityfor2,4-dichlorophenolwasatpH5.0–6.0for 270
bothfreeandimmobilizedfungalbiomass. 271
3.2. BioadsorptionkineticsofphenolonCa-alginatebeads, 272 immobilizedPh.chrysosporiumbiomass,andfreebiomassfrom 273
aqueoussuspension 274
Thebiosorptiontime ofphenolonto Ca–alginatebeads(2%), 275
alginate immobilized Ph. chrysosporium biomass, and free Ph. 276 chrysosporium biomass was evaluated with a solution contain- 277
ing 50mgL−1 of phenolat pH 5.5 in natural state withoutpH 278
adjustment.Thebiosorbentconcentrationwas0.3gL−1,thecon- 279
centrationofPh.chrysosporiumbiomasswas1.25%inthealginate 280
beads.Theinitialphenolconcentrationwas50mgL−1.Thechange 281
ofphenolconcentrationinthesupernatantispresentedinFig.3a. 282
In Fig.3b, theadsorbedamounts of phenol, and in Fig. 3cthe 283
adsorptionefficiency(inpercent) ispresentedagainstthesorp- 284
tion time. Fig. 3a–c demonstrate that the adsorption rate was 285
initially highin the very first minutes,and thesaturation was 286
reachedaftersixtyminutesforalltheadsorbentsstudied.Beyond 287
thattime,theamountofadsorbedphenoldidnotincreasesignif- 288
icantlywithsorptiontime.Atthebioadsorptionequilibriumwith 289
initialphenolconcentrationof50mgL−1,theadsorptioncapacity 290
was2.78mgg−1 on Ca–alginatebeads, 3.33mgg−1 onimmobi- 291
lizedbiomassand6.73mgg−1onfreebiomass.Fig.3calsoshows 292
thatapproximately13.45%ofphenolequilibriumuptakecouldbe 293
reachedwithinfortyminutesonfreefungalbiomass,andthatthe 294
correspondingphenolequilibriumuptakewas6.66%and4.85%for 295
immobilizedfungalbiomassandblankCa–alginatebeads,respec- 296
tively.Thissuggeststhattheadsorptionrateofphenolontothe 297
immobilizedfungalbeadswasslowerthanthatontothefreefun- 298
galbiomassintheinitialbiosorptionperiod.Inourstudy,thelow 299
adsorptionefficiencycan beexplainedwiththelow biosorbent 300
dosage.Wuand Yu[25] reportedthatapproximately78.03% of 301
2,4-DCPequilibriumuptakecouldbeachievedwithin30minon 302
thefreefungalbiomass,andthatthecorresponding2,4-DCPequi- 303
libriumuptakewas68.04%and71.24%fortheimmobilizedfungal 304
biomassandCa–alginatebeads,respectively,inthecaseofbiomass 305
dosageof5gL−1 andinitialconcentrationof40mgL−1.Wehave 306
toconsiderthattheadsorptionincreaseswithdecreasingwater 307
solubilityofthemoleculeandwithincreasingoctanol–waterparti- 308
tioningcoefficient.Thefreebiomasshaditsbindingsitesexposedto 309
phenol,whereastheentrappedbiomasswasretainedintheinterior 310
oftheimmobilizedbeads[20,25].Thetimeof60minwasconsid- 311
eredtobesufficientforphenolbiosorptiontoreachequilibriumfor 312
alltheadsorbentsstudied. 313
3.3. Kineticmodeling 314
Thereare severalkineticmodelsregardingtheadsorptionof 315
heavy metals, dyes and chlorophenols[3,7,31,32,34]. To evalu- 316
atethebioadsorptionkineticsofphenol,twokineticmodelswere 317
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Fig. 3. Time courses of phenol biosorption by Ca–alginate, immobilized Ph.
chrysosporiumbiomassbeadsandfreebiomassatpH5.5,T=22.5◦C.(a)Thephenol concentrationsarepresentedagainstthesorptiontime.(b)Theadsorbedphenol amountsarepresentedagainstthesorptiontime.(c)Theadsorptionefficiencyval- uesarepresentedagainstthesorptiontime.Theinitialphenolconcentrationis 50mgL−1andthebiomassdosageis0.3gL−1.Thebiomassconcentrationinalginate beadsis1.25%.ErrorbarrepresentsSD;n=3.
usedtofittheexperimentaldataobtainedonCa–alginatebeads,
318
Ca–alginateimmobilizedPh.chrysosporiumbiomass,andfreePh.
319
chrysosporiumbiomass.
320
3.3.1. Pseudofirstorder-Lagergrenmodel
321
Thepseudofirst-orderkineticmodel(Lagergrenmodel)isgen-
322
erallyexpressedasfollows:
323
dq
dt =k1,ad(qeq−q) (2)
324
Fig.4. (a)Linearizedpseudofirst-order kineticmodelfor phenolsorptionby Ca–alginatebeads,immobilizedbiomassinCa–alginateandfreePh.chrysosporium biomass.(b)Linearizedpseudosecond-orderkineticmodelforphenolsorptionby Ca–alginatebeads,immobilizedbiomassinCa–alginateandfreePh.chrysosporium biomass.Theinitialphenolconcentrationis50mgL−1andthebiomassdosageis 0.3gL−1.Thebiomassconcentrationinalginatebeadsis1.25%.Errorbarrepresents SD;n=3.
where k1,ad istheadsorptionrateconstant offirstorderbioad- 325
sorption(min−1),qisadsorbedamount(mgg−1),qeqisadsorption 326
capacity(mgg−1)atequilibrium. 327
IntegrationandlinearizationofEq.(2)give 328
log(qeq−q)=logqeq−k1,ad t
2.303 (3) 329
Theplotsoflog(qeq−q)vs.sorptiontimeareshowninFig.4a. 330
Thelinearrelationshipswereobservedonlyfortheinitial30minof 331
sorptionandtheexperimentaldataconsiderablydeviatedfromthe 332
theoreticalonesafterthisinitialperiod.Thesorptionrateconstants 333
k1,adandthetheoreticalvaluesofqeqcalculatedfromtheslopeand 334
interceptofthelinearplotsaresummarizedinTable1,withthe 335
correspondingcorrelationcoefficients. 336
Thesorptionrateconstantk1,advariedintherangeof1.15×10−2 337
to 6.91×10−2min−1. The first-order rate constants k1,ad are 338
5.13×10−2min−1forCa–alginatebeads,1.15×10−1min−1forthe 339
immobilizedbiomassand6.91×10−2min−1forthefreebiomass. 340
Thetheoreticalvaluesofsorptioncapacityqeqarelowerthanthe 341
experimentalvalues.Thecalculatedadsorptioncapacitiesqeq,calare 342
2.20mgg−1forCa–alginatebeads,1.81mgg−1fortheimmobilized 343
biomassand2.69mgg−1forthefreebiomass. 344
3.3.2. Pseudosecond-orderkineticmodel 345
Thepseudosecond-orderkineticrateequationcanbewritten 346
asfollows: 347
dq
dt =k2,ad(qeq−q)2 (4) 348
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Table1
Thepseudofirst-andsecond-orderrateconstantsandthecalculatedequilibriumadsorptioncapacitiesonfreePh.chrysosporiumbiomass,Ca–alginateimmobilizedbiomass, andCa–alginatebeadsatpH5.5.Ca–alginateconcentration:2%,thebiomassconcentration:1.25%.T=22.5◦C,biomassconcentration:0.3gL−1.
Biosorbent k1,ad(min−1) qeq,cal(mgg−1) R2 k2,ad(min−1) qeq,cal(mgg−1) R2 qeq,exp(mgg−1)
Freebiomass 6.91×10−1 2.69 0.946 4.27 6.85 0.996 6.73
Alginate+biomass 1.15×10−1 1.81 0.963 1.62 3.41 0.999 3.33
Alginate 5.13×10−1 2.20 0.852 5.47×10−1 2.94 0.996 2.78
where k2,ad is the rateconstant of second order bioadsorp-
349
tion(gmg−1min−1),qistheadsorbedamount(mgg−1),qeqisthe
350
adsorptioncapacity(mgg−1)intheequilibrium.
351
TheintegratedandlinearizedformofEq.(4)is
352
t q= 1
k2,adq2eq
+ t
qeq (5)
353
Fortheutilizationofthismodel,theexperimentalvalueofqeqis
354
notnecessarytobeestimatedapriori.Straightlineswereobtained
355
byplotting t/qagainstt for Ca–alginatebeads, for immobilized
356
biomassinCa–alginate,and freebiomass(Fig.4b).Thesecond-
357
order rate constants, k2,ad and qeq, are summarized in Table 1
358
andweredeterminedfromtheslope andinterceptof theplots
359
(Fig.4aandb).Thesorptionrateconstantk2,advariesintherange
360
of5.47×10−1to4.27gmg−1min−1.
361
The second-order rate constants, k2,ad, are
362
5.47×10−1gmg−1min−1 for Ca–alginate, 1.62gmg−1min−1
363
fortheimmobilizedbiomassand4.27gmg−1min−1 forthefree
364
biomass.Thelargestsecond-orderratevalue(4.27gmg−1min−1)
365
was obtained for the free biomass. The Ph. chrysospo-
366
rium biomass immobilized in Ca–alginate exhibits a higher
367
rate constant (1.62gmg−1min−1) than the alginate beads
368
(5.47×10−1gmg−1min−1).
369
Thetheoreticaladsorptioncapacitiesqeq,calare2.94mgg−1for
370
Ca–alginatebeads,3.41mgg−1 fortheimmobilizedbiomass,and
371
6.85mgg−1forthefreebiomass.Thecalculatedadsorptioncapac-
372
ities agreed well with the experimental data. The correlation
373
coefficientsforthepseudofirst-orderkineticsmodelwerelower
374
thanforthepseudosecond-orderone.
375
Fromthecomparisonofthetwokineticmodels,wecanconclude
376
that thebiosorption process of phenol onto the surface of Ca-
377
alginate,immobilizedPh.chrysosporiumbiomass,andfreebiomass
378
followsthepseudosecond-orderkinetics.DursunandKalayci[35]
379
studiedthephenoladsorptiononchitinfromaqueoussolutionat
380
abiosorbentdosageof1gL−1(29).Theyfoundthattheadsorp-
381
tion process followed pseudo second-order kinetic model, and
382
theadsorptionrateconstantvariedintherangeof3.9×10−3to
383
4.510−3gmg−1min−1at20,30and40◦C.
384
3.4. BioadsorptionisothermsofphenolonCa–alginatebeads,
385
immobilizedPh.chrysosporiumbiomass,andfreebiomassfrom
386
aqueoussuspension
387
Thebiosorptionisotherms of phenolonto Ca–alginatebeads
388
(2%),immobilizedPh.chrysosporiumbiomassinCa–alginate,and
389
freePh.chrysosporiumbiomassweredeterminedbyvaryingtheir
390
initialconcentrationsintherangeof10–100mgL−1 withacon-
391
stantadsorbentdosageof0.3gL−1atpH5.5innaturalstatewithout
392
pHadjustment.ThePh.chrysosporiumbiomassconcentrationwas
393
1.25%intheCa–alginatebeadsandtheCa–alginateconcentration
394
was2%.InFig.5aandbthechangeofadsorbedamountofphenol
395
onalltheadsorbentsarepresentedagainstequilibriumconcen-
396
trations.Thefreebiomasshasahigheradsorptioncapacitythan
397
theimmobilizedbiomassin Ca–alginateand theblankbiomass.
398
Theexperimental maximumadsorbed amountwas3.27mgg−1
399
forblankalginatebeads,7.81mgg−1forimmobilizedbiomassin
400
Ca–alginateand13.50mgg−1 forthefree biomassattheinitial
401
phenolconcentrationof100mgL−1.Theexperimentalresultsare 402
compared withother studiessuchas bioadsorbentand adsorp- 403
tioncapacityinTable2.Biosorptionof2,4-dichlorophenolbyfree 404
Ph.chrysosporiumbiomass,immobilizedbiomassinalginate(2%) 405
andalginatebeadsfromaqueoussuspensionswerestudiedbyWu 406
andYu[25].Thetheoreticalmaximumadsorptioncapacitiesdeter- 407
minedfromtheLangmuirmodelwere1.63,4.55,and7.15mgg−1 408
fortheblankCa–alginate,immobilized,andfreefungalbiomass, 409
respectively. 410
3.5. Modelingtheequilibriumofbioadsorption 411
Among the zillions of two- and three-parameter isotherm 412
equations, two simple models are frequently used to describe 413
biosorptionprocesses[3].Toevaluatethebiosorptionisotherms 414
ofphenol,weusedtheFreundlich,Langmuir,andanti-Langmuir 415
[36]modelstofittheexperimentalequilibriumdatadetermined 416
onblankCa–alginatebeads,immobilizedbiomassinCa–alginate 417
beads,andfreePh.chrysosporiumbiomass.Inthisstudy,thenon- 418
linearleast-squaresestimationandthelinearizedpresentationof 419
isothermequationswereusedfortheevaluationofbioadsorption 420
equilibrium.Intheresearchfieldofbiosorption,thelinearizedpre- 421
sentationofisothermequationshasbeenfrequentlyusedforthe 422
determination ofbioadsorptionconstants despiteofits hazards 423
[3,37].Wepresentacomparisonoftheequilibriumconstantscal- 424
culatedfromthelinearizedand original,nonlinearformsofthe 425
isothermequations. 426
3.5.1. Freundlichisothermmodel 427
Thewell-knownFreundlichmodelisexpressedasfollows: 428
qeq=KFCe1/n (6) 429
whereqeqistheadsorbedamountintheequilibrium(mgg−1);KF 430
istheFreundlichconstant(mgg−1);Ceequilibriumconcentration 431
ofphenol(mgL−1) 432
LinearizationofEq.(6)gives 433
logqe=logKF+1
nlogCe (7) 434
Theplotsoflogqe againstlogCe areshowninFig.6a.Wehave 435
comparedtheFreundlichconstantscalculatedfromthelinearized 436
presentationof theisotherms with thenonlinear least-squares 437
estimates(Fig.5aanda,Table3)[37].ThevaluesoftheFreund- 438
lichconstant KFand theexponent n calculatedby Eqs.(6) and 439
(7), respectively, and the correspondingcorrelation coefficients 440
aresummarizedinTable3.Fromthelinearizedpresentationthe 441
Freundlichconstant,KFvariedintherangeof0.023–0.203mgg−1. 442
The Freundlich constants KF are 2.03×10−1mgg−1 for free 443
biomass, 4.73×10−2mgg−1 for the immobilized biomass, and 444
2.30×10−2mgg−1forblankCa–alginatebeads.Theorderofmag- 445
nitude of KF was: free fungal biomass>immobilized fungi in 446
Ca–alginatebeads>blankCa–alginatebeads.Thisorderindicates 447
ahigheradsorptioncapacityofthefreeandimmobilizedfungal 448
beadsovertheblankCa–alginatebeads.Forfreebiomass,thenval- 449
uesweregreaterthanunity,indicatingafavorableadsorption.For 450
immobilizedfungalbiomassandblankCa–alginate,thenvaluesare 451
closetounity.Thevaluesofexponentnare1.16forfreebiomass, 452
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Fig.5.(a)Fittedphenolbioadsorptionisothermsfromnonlinearleast-squareestimationusingFreundlichequation(b)datafromnonlinearleast-squareestimationusing LangmuirequationbyCa–alginatebeads,immobilizedPh.chrysosporiumbiomassbeadsandfreebiomassatpH5.5,T=22.5◦C.(c)PresentationoftheFreundlichand(d) Langmuirisothermsusingcalculateddata.Theadsorbedphenolamountsarepresentedagainsttheequilibriumconcentrationofphenolafterthebiosorptionprocess.Error barrepresentsSD;n=3.
0.93fortheimmobilizedbiomassand0.91forblankCa–alginate
453
beads.
454
The estimated values of constant KF using nonlin-
455
ear least-squares fitting are 2.92×10−2mgg−1 for free
456
biomass, 8.73×10−3mgg−1 for the immobilized biomass, and
457
3.70×10−2mgg−1 for blank Ca–alginate beads. The estimated
458
values of exponent n are 0.75 for free biomass, 0.67 for the
459
immobilized biomassand 1.01for blankCa–alginatebeads. For
460
bothfittingmethodsthecorrelationcoefficientsareratherhigh.
461
InFig.5c,theexperimentallydeterminedandthefittedisotherms
462
–using theFreundlichconstants calculatedfromthelinearized
463
isothermequation–arepresented.Nevertheless,wecanconclude
464
thatthenonlinearleast-squaresestimationusingtheFreundlich 465
modelgivesbetterfitandmoreauthenticresults(Fig.5aandc) 466
thanthelinearization. 467
3.5.2. Langmuirandanti-Langmuirisothermmodel 468 TheLangmuirmodelisvalidformonolayeradsorptionontoa 469
surfacecontaininglimitednumberofidenticalsites[3].TheLang- 470
muirisothermmodeliswritteninthefollowingform: 471
qeq=qmax KLCe
1+KLCe (8) 472
Table2
Comparisonofbiosorptioncapacityonvariousbiosorbentsforphenolanditsderivatives.
Typeofadsorbents Pollutant Equilibrium
time
Pollutant/adsorbent concentration(gL−1)
pH Adsorptioncapacity References
Pseudomonasputida Phenol 48h 0.6/1 7.0 22%phenolremoval [38]
Caulerpascalpelliformis Phenol 6h 0.1/6 6.0 20.1 [39]
Fumaliatrogii Chloro-phenol 6h 0.5/20 8.0 289.1 [40]
Pleurotussajorcaju Chloro-phenols 4h 0.5/0.2 6.0 0.95–1.89 [41]
Activatedcarbon Phenol 10days 1 6.0 1–31 [42]
Bacillussubtilis Phenol 30min 0.015/25 7.0 0.06 [43]
Chitosan–calciumbeads Phenol,chloro-phenol 4h 0.3/1 7.0 116.31 [44]
Aspergillusniger Phenol 24h 0.001/2 5.1 0.6 [31]
Driedsewagesludge Phenol 24h 0.1/5 6.5 17.3 [45]
Phanerochaetechrysosporium Phenol 24h 0.1/0.3 6.0 13.5 Presentstudy
Ca–alginatebeads(2%) Phenol 24h 0.1/0.3 6.0 3.27 Presentstudy
ImmobilizedPhanerochaetechrysosporium Phenol 24h 0.1/0.3 6.0 7.81 Presentstudy
Phanerochaetechrysosporium 2,4-DCP 6h 0.04/5 5.0 3.22 [25]
Ca–alginatebeads(2%) 2,4-DCP 6h 0.04/5 5.0 0.93 [25]
ImmobilizedPhanerochaetechrysosporium 2,4-DCP 6h 0.04/5 5.0 2.13 [25]