workers and assess their efficiency for different rnetal bearing solutions and industrial efiluents .... whether some others, such as Al, Ag, Cd, Sn, Au, Sr Hg, Ti.
JournalofIAEM,VoL37(2&3), (2010) 142-162,
BIOSORBENTS FORREMEDIATIONOFHEAVYMETALSBEARING EFFTUENTS: A REVIEW DILIPMARKANDEYI,RAJK. SATARZ,N. MARKANDEY3 ANDR.C.TRTVEDT
ABSTRACT : The biosorption of heavymetalsby microorganisrns hasbeenrecognized and well established asa potentialalternative to existingtechnologies for removalandrecovery of rnetalsilom aqueous wastestrearns. Moststudiesof biosorption for rnetalremovalhaveinvolvedtheuseof either laboratory-grownmicroorganismor waste biomassgeneratedby the units like fermentation, antibioticproduction, pharmacological units,fbod processing industries, wastewater treatment units etc.Manymicroorganisms cantakeup dissolved rnetalsfiom theirsunoundings ontotheirbodiesand canbe usedfor rernoving healy rnetalionssuccessfully. Equilibriumstudies thatgivethecapacityof adsorbentand the equilibriumrelationships betweenadsorbentand adsorbate are describedby adsorptionisothermswhich are usuallythe ratio betweenquantityadsorbedand the residualin solutionat equilibriumstate. Examination of the publishedliteraturealso revealsconvincingevidencethat a wide varietyof microorganisms havebeenfeportedto accumulate largequantities of heavymetalslike Au, Ag, Cu, Cr, Co,Cd,Pb,Hg, Ni, Mn,Zn, etc.Theseuniquemicrobiological characteristics in nowwell studied andusedon a laboratory scalefor scavenging thesecontaminants from synthetic solutionas well as from certaindilutedindustrialeffluents.In suchrernediation sys(em, microbes areusedin viableas well asnonviableconditions. Now, voluminous infonnationis available on theuseof algalvariables like Spirogtra, Ulothrix, Chlamydomonas, Chlorella, Nostocetc.,fungal isolateslike Aspergillts, Rhizoptts,Mucor, Trichoderma,Penicillium, Volvoriella, Phoma etc., bacterial isolai.-s like Pseudomonas, Mycobacterium,Streptomyces,Bacillus etc and actinomycetes-and yeast like Saccharomyces, Candidaetc.An attempthasbeenmadeto collatethe factsandfindingsof various workersandassess theirefficiencyfor differentrnetalbearingsolutions andindustrial efiluents Keywords:biosorption,heavymetals,copper,lead,zirrc.free-and imrnobilized biomass, fungi; bacteria; bioaccumulation;environmentalvariables, sorption efficiency, mycelial waste, '' decontarnination
INTRODUCTION Thoughthe metalsare an intrinsiccomponentof the environment, the prqsence of variousmetallicformsis regarded asa peculiarin thesensethatis difficultto remove them completely,once they enter into it. Ir{ineralsand surfacedepositsand their erosion,forest fire, volcanic activitiesetc. are someimportantnaturalsourcesof these 't. contaminants Witl'rincreases in theuseof a widevariety of metalsin industries as well as our daily life, problems arisingfrom theseas metal pollutionl-5. Urbanization, modern agriculturalpracticesetc. are also equally responsible for suchtypeof pollution.In soil,around90 %, of heavy metalscome from Zn, Fe and other types of smeltersetc. Becauseof use of fertilizers,pesticides, insecticides etc. in agricultural, increased concentration of Cd. Ptr,Hg etc.canalsobe seen,which arealsoultirnately o-10" responsible fbr ecological imbalance To a largeextent, thesemetalliccontaminants are dispersed in thebiosphere tlrough various types of industrialeffluents,municipal
wastewaters,transport,power generarionetc. Another irnportantmeansof their dispersalare the movementof drainagervaterfrom the run off of catchments,which have been contaminated by wastefrom mining, c;e dressing, metallurgicalactivitiesand other kno',rn and unknorvn sources. The termheavymetalhasfoundits way into theR & D programme all overthescientificworld ll-r7.Although no prccisedefinitionis renderedyet, in general,theseare metalsrvith atomicnumbergreaterlhan23 and densities, mare than 5, (except Be, and S*). There are nonbiodegradable and persistin natureof a long periodand toxic to living organisms at f-airlylow concentration. The expression of heavymetalsis often use wheretheseare connotation of toxicity.Manya time,peihapsuncertain of definitionemploysthe lessevocativetermstraceelements 't-'o Th.seareconsidered ascontaminant. Because of their greatpotentialities to aquaticecosystem, thcsehavebeena subjectof extremeimportance in the last ferv decacles, althoughthe negativeimpactsof thesecontaminants on
sprcsent 1.4: CtrntralPttllutioh ControlBoard,ParivchBhavan, * CpCB,ZonalOfce- West,Opposire F-rstArjur Nagar,Dclhi 110032. addrcss VMC, Ward rCoresporrding No I0. Subhanpum' Vadodara 290023, Fax(0265)2392987 aurhor, e-mail: dilinkmrark(dyahoo.corn. "
t4)
MARKANDEYetal. SIGNIFICANTTOXIC-ANDPRECIOUS TABLEI: CHEMICALQUALITIESOF CERTAINENVIRONMENTALLY METALS in Atomic Metal Atomic Atomrc Density Melting Boiling Frequency nature radii,pm pointoC pointoC number mass
Ionic radiation
EIV*
sb
95
243
11.3
994+4
1750
0.0001
145
76(1ll), 62(v)
,1.82
As
33
74.92
5.73
817
613
0.0005
t25
58(l l1),a6(v)
Be
4
9.012 1.86
1278+5
2.20 -1.2
Col
48
ll2.4l
320.9
58.78
0.00016
119
196(1),47(v), 39(vii)
2.74
Cr
24
51.994 7.19
1857+202672
0.02
125
63(lll),52(vi)
l.s6
Co
27
58.934 8.83
l49s
0.0023
125
72(rr),63(11l)
r.70
Cu
29
63.546 8.93
1083.4 2563
0.007
128
96(r),72(rt)
r.7s
Au
79
196.96719.3
1064.4 28.3
0.000,000,05 144
1 3 7 ( i8) ,5 ( l 1 )
r.42
Fe
26
55.841 7.84
l 535
2750
5.0
124
74(lr),64(11l)
1.64
Pb
82
207.2
327.5
1740
0.0016
l'75
2 1 5 ( -l )l , 1 2 0 (l l) , 8 4( r 1 )
1.55
Mn
25
54.938 7.3
il8
80(ll),66(lll),a6(vii)
1.60
Hg
80
0.1 1244+3 1962 200.s9 13.55 -38.87 356.58 0.0005
150
lr0(lr)
r.44
Mo
42
95.94
10.2
26r7
4612
0.0015
72(lll) 62(vi)
1.30
Ni
28
58.70 8.90
1453
2732
0.008
6e(ll)
r1s
Pt
78
195.09 21.45 t . 7 7 2
80(ll), 65(vi)
r.44
Se
34
78.96 4.8
2t7
Sn
50
I 18.69 7.3
231.97 22',t0
0.004
140
294{-iv),93(ii) 7l(iv)
r.72
Ag
4'7 '14
10'1.87 10.5
96r.93 2 2 r 2
0.00001
144
1 2 6 ( 18)9, ( r )
r.42
136
70(iv),62(vi)
1.40
8.64
11.4
2870
3827+100.0000005 1 3 8 684.9
0.000009
v
23
183.85 19.30 3410+205 1 6 6 0 0.007 1g9Q+103380 0.015 50.942 6.1
Zn
30
65.38 7.2
w
124
4 1 9 . 5 8 907
0.013
191(ll), 83(ll), 50(vi),42(vi) 2.48
88(ll),74(ll1),63(iv), 59(v) 1.45 133
74(n)
r.66
* electronegative values living being havebeenknown for a very long period,it is only in recentyears,however,that public concernspuned asoutbreaks of Minamata,Itai- Itai in by variousincidences Japanand similar symptomsobservedin lraq, Pakistan, Guatemalaand Nerv Mexico etc, Similar caseswere also in reportedin India.Specificto this are Cd contamination in Rajpur,Cr in KanpurandTamilnadu,Mn contamination in West Bengaletc.,which has Unnao,As contamination led to the introductionof strict regulatorymeasures govemingof thesemetalsll-al. In the recent,the term healy metalsdescribethe presences of As, Cd,Sb,Be,Cu,Co,Cr, Mo, Ag, V, W, Ni, Pb,Fe,Hg,Zn etc.It hasbeenfelt thatthe impactsof these even highlydisastrous contaminants to theaquaticresources I -1'4 14'54. Though,someof the if theyarepresentin traces metalions like, Cu, Mn, Zn, Fe, etc. are also servcas a micronutrientsand are requiredfor plants and animal, includinghumanbeing,while somemetalionslike Cr, Pb, Ni etc. are hazardousand createscomplicationsin the ecologyof thereceivingsystemetc.andsomeof themetals
e.g.Ag, Au, Pt, W, Th, etc.highlypreciousin nature.Table I highlightsimportantchemicalcharacteristics of certain toxic-andpreciousmetals,which are of environmentally significant. These occur in various forms in aquatic environment andrangesfrom finely dividedmetalparticles dissolved to and ionizedmetal ions. In the ionic forms furtherit occursascations like Co2*.Cu2*.Cr6*.Zn2r.Fe3'. Hg2',^Pb2', Cd2',Ag* etc.as well as certainanionslikc Cr2Ol'. These appearin the effluent of a variety of processes. In additionto municipalwast€water, industrial operations like electroplating,battery manufacturing, pigment- and paint production,tanneryetc. contribute significantamoun[of thesemetalsin the aquaticsystem. Thesecontaminants find theirway into thereceivingaquatic systemthroughvarious'naturaland andmanmadesources lead to severalundesirable effectson naturalresources. They canbe discharged into sewersgive riseto high metal
143
BIOSORBENTS FORREMEDIA]ION amountofthese recyclingprocessalsoreleasesconsiderable metals on land, which ultimately reaches to aquatic resourcesthrough run-off. In applying sewagesludgeto agriculturalland, it initiatesa reversalof this functionwith thegraduallurning into the new siniHg>Pb>Cu>Ni>Cd> Mo= CO =Zn
Ps.stutzeri
PSS
U>Pb>Hg>Cu>Cd>Co >Mo=Ni =Zn
Zooglearomigera
ZR
U>Hg>Cu>Pb>Ni>Mo : Co=Cd=Zn
Actinomycetes flavovitidis ulbtts Streptomyces
AF
U>Pb>Hg>Cu>Zn>Cd :Ni>Mo=Co
SA
U>Hg>Cu>Pb=.Cd >lvlo=Ni>CeZn
The mostof industrialeffluent are acidicin nature and most of the metalsremainin the dissolvedform. The solubilityof differentmetalsoccurat differentpH valuefor multimetallic system a single pH which can produce sufficiently low solubility of al metal ions has to be estimated.Somemetalstend to solubilizebeyonda certain optimum range.For somemetalse.g. Cr (VI) conversion form onestateof oxidationto anothermay be requiredprior to precipitation.In caseof Cr, thehexavalentform mustfirst to be reducedto trivalentfbrm.
U>l{g>Pb>Cu>Mo: C o ' =N i > Z n U>IIg>Cd>Zn= Pb>Cu>Mo>Co= Ni
NON-VIABLE BIOMASS, SPENT MYCELIA FOR METAL REMOVAL Microbes mediatedremediatereactionsresult in significantmetalremoval,whenthe sameare usedin nonviablestate.In fact. thereare severalreportsindicatingthe rate of metal decontaminationis much higher which physicallyor chemicallykilled microbialcellsare usedto perform the said task. In addition to this following other advantages include-
SC
U>Hg>Pb>Cu>Cd>Mo =Ni>Co>Zn
Streptomyces echinatus
SE
U>Hg>Pb>Cu>Cd>Ni> Mo>Co>Zn
levoris Streptontyces
SL
U>l{g>Pb>Cu>Cd>Ni> Co=Mo>Zn
of differentmicroorganisms The overallperformattce vasrecordedin thefollowingmannerAF> BS> PSS> SE> > SL > SC> Zn
-
for controlledspacerequiretnent
-
longerdurationofstorage
-
Streptontyces cineorubor
;A> vll
16.8mg/gCd, 2.2mglgCu, 8.6mglgZn 5.6mg/gCd, 2.7nglgCu, l.l,mglgZn.
SOLUBILITY OF METAL IONS
Preferences of metal tons
Bacillus subtilis
METAL
Similar to specificity of microorganisms,the metabolicstateof theorganismsalsoplaysan importantrole in the metal accumulationprocess.Falla et al.E5conducted experiments on accumulationof metalsViz. Cd, Cu, Zn on Pseudomonas fluorescensusing"during"- and"aftergrowth phases".The performanceof variousstateswith respectto differentmetalswasobservedin following manner:-
is Transformingmetalvalencesby microorganisms rotherimportantareaofresearch.It hasbeenreportedthat s from wastewatercanbe removedby oxidizingAs III to rr5).Instead of chemicaltreatment, s V usingpyrolusite(e6' putida, Ps. Ps. alcaligenes,Ps. as such bacteria As Le purpose. The microbes itrophuscan be utilized for this Similarly,Removalof ruld oxidizeup to 29 /L of arsenate. r by changingfro Cr, (VI to Cr (III) by reduction,a ricroorganismssuch as Bacterium dechromations in raerobic environment or Ps. mendocina in aerobic attemptto adopt rvironrnenthaveprovedas an successful these of metals. Since cell dcrobesfor decontamination 'all compositionaredirectlyresponsible for uniquesurface 102 Nakajima and Sakaguchi havereported haracteristics, :lective accumulationof variousmetalions like Mn, CO, Ii, Cu, Zn, Cd, Hg, Pb, U etc. by certain test in the following manner:ricroorganisms Microorganisms
AI\D
PS=
4.61 4.41 4.41 4.31 i.83 492 1 . 3 2 = 4 . 3 2 4 . 147. 0 6 3 . 3x3 l 0 . an r o V g 149
to shockloadingetc. lesssensitive rr9'"tstudiedmetaladsorbing of capacity Azabet al. under some non-viable biomassesof nticroorganisms defined environmentalcondition and comparedwith conventionaladsorbentslike activated charcoal, ion exchangeresin.They have testedmaterialderivedfrom Aspergilltrs terrLts,Mttcor rarnannianus,Zvgorrhynchus, heterogantus, RhizopttssexLtlisandPenicilIium capsulatum, naturalcompost,Irishpeat,peantltshellu'all nul shell'bone etc. They observedrelativelyhigher efficiencyof theses to ion exchange as corupared adsorbents ncn-conventional non-conventional When etc. resin, activated charcoal treatedby alkalito provideadditionalsurfacefor adsorbents binding the metals, the efficiency of remediation theuseof localwastematt€ras Theysuggested accelerated.
BIOSORBEN'I'S FORREMEDIATION they are easily availableand cheap.Furthersuch type of applicationreduccsthe disposalproblemsof the later,e.g. thousands oftons ofspent mycelialaregenerated everyyear from antibiotics and fermentationindustries,biological effluenttreatmentplantetc.In general,thebioremediation is quite a complexproblen:dnd is governedby a wide variety 64'106' 107' 'oe. parameters of physicochemical As mentioned abovethat the pretreatment of biomasswith organicand or inorganicreagents,metaVbiomassconcentration raticn and pH, temperaturehas considerableeffect on the metal decontamination efficiencyof thesebiologicalvariables. The studiesconductedlls-r22 for the removalof Pb, Cu, Cd and Zn frirm aqueous environment using Aspergillus oryzoe,R. oligosporus,R. arrhizus,it hasbeenreportedthat the lab scalethe efficiency of the best isolateR. arrhizus wasmaximumfor Pb andminimum for Zn. The absorption patternwasobservedin followingmannerPDCu>Zn Wastemyceliafrom industrialfermentationplants (4. niger,P. chrysogenum and C.paspali)wereusedto asa biosorbent for removal of Zn ions from aqueous environments, bothbatchwise as well as in columnmode. Under optimizedconditionsA. niger and C. paspali were foundsuperiorto P. chrysogerutm'r'Removalof Pb ions fromaqueous solutionby non-livingbiomassof Penicillium chrysogenum wasstudiedandobserved thatPb wasstrongly affectedby the pH in the rangeof 4-5. Uptakeof Pb was 116 mglg dry biomass,rvhich was higher than that of activated carbon and some other microorganismsr2a Chrorriumbiosorptionby non-livingbiomassof Chlorella vulgaris, Clodophora crispate, Zoogloea ramigera, Rhizopus arrhizus and Saccharomlcescereyisiae was studiedand observedthat optimuminitial pH (1.0-2.0)of themetalion solutionaffectedthe metaluptakecapacityof thebiomassfor someselected microbialisolates. Maximum adsorptionratesof metalions to microbialbiomasswere obtainedat temperaturein the range of 25-150C.The adsorptionrates increasedwith increasingthe metal concentrationof Chlorella lulgaris, Clodophorucrispata, Zoogloea ramigera, Rhizopusarrhizu.sand Succharom.r-ces c e r e v i s i auep t o 2 0 0 , 2 0 0 , 7 5 , 1 2 5 a n d 1 0 0 m g l L 125 respectively Deadcellsof Sacclr arom)tces ceret,i.\i(te are also able to relnove upto 400/omore U or Zn than the correspondinglive cultures. Biosorption of U by Sacchat'omyces cerevisi(rervas a rapid processreaching 60% of the flnal uptakevalue rvithin rhe 15 minutesof contacttime. The deposition differingfrom that of other heavymetalsniore associated with the cell r.r,all,uranium tvasdeposited asfine needle-like crystalbothon insideand e0. outside the Succhoroml;gs.1 ceret,i.siae cells For the removalHg andCd severalbror.l'nsear,l eedswere testedfor theirabilityto removemetalionsfrom aqueous solutionby biosorptionand 90-95ozir rernovalievel was fbunclfrom
r50
e'. industrialwastewater Lr*ro minor, duckweedhasalso beenstudiedto removethe solublePb from water.Result shorvedthat viable biomassremoved85-90%of Pb while non-viableremovesthe 60-75%of Pb 126. Maximal removal of Ni from electroplating industriesoccunedby 2.5 gm of biomassof Saccharomyces cerevisaewithin the five hoursof exposure.The Ni uptake capacity from aqueoussolution was also studied in filamentousfungi suchasRhizopussp.,Penicilliumsp. and Aspergillus.lp.The metal uptakewas highestby Rhizopus .sp.amongall the testedmicrobialisolatesr0s.The yeast biomassSabcharomi:ces cerevisiaewhich is a by-product from breweryindustrywas usedfor purificationsof water pollutedby uraniumions,whichhadan efficiencyto absorb tJ 2.4 m Mol pgldry biomassr:t.Dead biomassof actinomycetes, which is the wasteproductfrom industrial fermentation, rvasmixed with wastewaterasa freebacterial suspensionand biosorption occurred. Cadrniurncations boundto negativechargedsiteson bacterialcell wall and couldbe desorbedr?8-r2e. The Cd (II) biosorptionto nonliving biomass of Rhizopus arrhizus and Schizomeris leibleniiwere also studiedin batchmode.The maximum adsorption ratesof Cd (lI) ionsto microbialbiomass wereat 30oCandat theoptimurnpH 5.0for bothmicroorganisms. The adsorptionratesincreased with increasing Cd (II) concentrationfor trt'hizopus arrhizus and Schizomeris leihleniiup to 100-150 mg/L respectively. The adsorption for Rhizopusarrhizusu'as higher than that of Schizomeris teibleniit:'ta.Dry cellsof Rftrzopus arrhizushasbeenused for theremovalof Iron (ll), Pb (lI) andCd (II) ionsfromthe industrial waritelvater.Higher adsorption rates and adsorptioncapacities were obtained at initial metal concentration up to 100 mg/L in batch reactor.High concentration of heavymetalionsmay bepurifiedby using multistagebatchreactorin series'''tn Biosorptionstudies werealso carriedout with the white-rotfungiPo[yporous versicolorandPhanaerochaete chrysaporium for Cu (II), Cr (III), Cd (ll), Ni (II) and Pb (II) under sameoperating conditions.F'.esultshowed that both were effectivein removingPb (ll) from aqueous solutionswith maximum biosorption capacityof 57.5 and I l0 nrg Pb (ll)ig dry biomass". Mr,ro, meihi, a fermentation industrialwaste rvasfc,undto lre effectivebiosorbentfor the removalof hexavalentch,nlmiumfrom industrraltanningeffluents. Sorytion levelsof 1.15and0.7mmol/g rvereobserved at pII 4 and 2 respeclively.In comparisonrvith ion- exchange resins.Mucor blomassdemonstrated Cr biosorption levels that correspond closelyto thoseof commercial strongly acidicexchange resils,whilepII behavior mirrored thatof rveakly acidic resins in solutions.The Cr elution characteristic from Mucor biomassrvassimilarto thoseof bothweakll,and strongly aciclrcsins''].
MARKANDEYet al. Wastebiomassfrom pharmaceutical fermentation industry,i.e. non living Rhizopusnigricanshasbeenused for adsorption of Pb over a range of rretal ions concentration, adsorption time,pH andco-ions.Theprocess of uptake obeys the Langmuir and Freundlichisotherms. Comparisonof uptakebetweenNaOH-treated anduntreated biomassshowsthat theadsorption takesplacein thechitin structureof the cell wall r30.The biosorptionof Cu (II), Ni (II) and Cr (VI) from aqueoussolutionon dried algae (Chlorella vulgaris, Scenedesmus obliquus trnd Synechocystip sp.) were testedunder laboratoryconditions as a function of pH, initial metal ion and biomass concentration. Experimentresultsshorvedthat influenceof thebiomassconcentration on metaluptakeof all thespecies. Both Freundlich and Langmuir adsorptionmodels rvere found to be suitable for describing the short term biosorptionof Cu (II), Ni (lI) and Cr (VI) by all algae e7. species
pH valueof 4.0 in adsorption periodof 4.0 h at 36+2oC, carbondosesof 16.0t/L when the initial Ni concentration was25 glL"'. CHOICE OF SORBEENTFOR REMEDIATION A considerableamountof informationis available on the choiceof sorbentsof variousorigins.It includesthe useof algae,fungi,bacteria, yeast,aquaticplants,biological and agricultural material, fly ash etc. Briefly it is summarizedin the followingmanner:-
USE OF FRESH WATER AND MARINE WATER ALGAE Benderet al l3adevelopedcyanobacterial mat in a glass column and observedtheir efficiencyto removeZn and Mn presentin the compositedslnthetic wastewater. They observedthat the developedimmobilizedcell system efficiencyremoveZn (96%)andMn (85%)at retentionrime of 3 h. Final zinc and Mn concentration in thenat (mg/g) Non-living wastebiomassfrorn Aspergillusniger were 10.13 and 10.30 respectively.Cai et a1.25used along with rvheatbran was used as a biosorbentfor the lyophilized uniceliular alga Chlamydomonas. reinharadtii removalof Zn andCu from aqueoussolution.The binding for removalof Cd from solution.When the algalcells are capacityof biomassfor Cu wasobservedto be higherthan treatedu'ith phytochelatinsynthesisinhibitor buthimonie that of Zn. The metaluptakervasfoundto be a functionof sycloximine,the rate of accumulationof ttre Cd got theinitialmetalconcentration, biomassloadingandpH. The accelerated by 3 folds.They havediscussed theirfindingsin metaluptakeof Cu by biomassdecreased in thepresence of contextof enhancing themetalbindingcapacityof algaeby Co- ion. The uptakeof Cu by biomassdecreased in the expressionof foreign metallothioneingenes-Matheickalet presence 16 of the Zn andvice versa.The decreased in metal al conductedsomebatchand columnexperiments with uptakervasdependson concentration of metalionsin two marine alga Durvillaea potatorum by treating it with compoundsin aqueoussolution 80. Dried, nonliving, calcium chloride and subsequently thermaltreatmentto granulated biomassof Streptoverticillium cinnamoneum was remcveCCfrom syntheticsolution.At solutionpH of 5, the usedfor the recoveryof Pb andZn fi'cn the solution.The maximumadsorptioncapacityof the pre treatedbiomass optimum pH of Zn and Pb was 3.5-4.5 and 5.0-6.0 wasfound l.+ m moVg.Thekineticsfor Cd adsorption was respectively.The maximum loading capacity of S. fastwith 90%of adsorption takingplacewithin30 rnin. cinnamoneum biomasswas57.7 mg/gfor Pb and21.3m{g Ye et al. 15studiedthe metaluptakecapacities of for the Zn with boiling water pretrearment.The loaded biomasses of certaincommonmarinemacroalgae.They metalscouldbe desorbed effectivelywith diluteHCI, nitric observed that the maximum uptake capacitiesof the acidand0.1 M EDTA. Treatment u'ith 0.1 Iv{Na carbonate biomassrangedfrom around0.8 to 1.6 m moUg(dry), permitted reuse of desorbedbiomass though loading '''. rvhich were much higher ihan those of other types of capacity in subsequent cyclesdecreased by 14-37% Th. biomass.Using two stagedbatchreactor,Aksu et al. (tt) non-living free and inrmobilizedbiomassof Rhizopus have studiedthe biosorptionof Cr (VI) on Cladophora arrhizu.swas used to study biosorptionof Cr (VI). crisputa in lab.The sorptionphenomena wasexpressed by Chronriumrernovalrate$,asslightlymorein freebiornas_q the FreundlichIsothermand this expression u,asusedfor conditionsover immobilizedstate, Stined tank reactor the calculation of the equilibriumvalueof theresidualor studiesindicatedrnaximumcluontiumbiosorption at 100 (\zI) adsorbed Cr concentration (C.oor C,o)at eachstagefor -liquid rpnrandat I:10 biomass ratio.Fluidizcdbedrcactor given quantity a of algae/ volumeof waste.lvater containing is more efficient in chrorniumrenrovalover stirredtank (VI) (Xoivo) Cr or ratio in a two staged batch reactor. The reactor.Immobilization of biomaterial hasliiiJr,effecton the ttz. n metallic ions andalealcell wall chromiumbiosorptionby Rhizopuscrrhizus Wheal l.rs. Usingmarinealgisargassu* stemandbabulbark,a raw lnaterialwasuscdasagrrrn aste 2 etc. "0, Nustocmuscorum have carbonsto removalthenickelmetaifronrtheeffluentof the alsoreportedbv variousinvestigators. Table3 summarizes electroplating inclustry.Electroplating \','astewiitcr showed certainsignificantpiecesofresearches conducted by various 2%-10% lower removal as comparedto the synthetic workers on the uses of algae for removal of some of these solutions asthesimilarconditicns. Ahnosl100-ol, rernoval of metals from aqueous environment. usingwheatstemiictivatedcarbonat a Ni (ll) wasobserved 151
BIOSORBENTS FORREMEDIATION TABLE3: ALGAL VARIABLESFORREMOVALOFVARIOUSHEAVYMETALS AIgae
Effrciency/comments
Metal
Reference
Chlamydomonas reinhardtii
Hg,CdandPb
effrcient
30
Chlorella vulgails
Pb
effective
19
Cystoseiraindica
U
Significantremoval
5l
marinealgal biom,ass
Cu
effective
60
seaweeds:
CoandNi
Promisingculture
139
brown marine dga Turbinaria ornatas
Cu
effrcient
140
Ulvafasciata sp
Zn
effective
5
Ulothrixzonata
Cu
effective
I
Sargassumsp.
Cu,Cd,Zn
Resistance
63
Sargassumsp.
Cu,Cd,Fe
2.3 meqg
Cladophoracrispata
Cr(VI)
Co2lLlmglk,Ceq130mg/L
12
Cladophoracrispata
c(vr)
Follw-freundandLangmiur
13, 14
Marine macroalgae
Cd,Cu,Pb
0.8-16mmoVg
46
Durtillea potatorum
cd
l.l mmoVg90% 30 min.
16
AnabaenadoliolumChlorellawlgaris
Cu,Fe
Immobilizedefficientupto3 repeats
l7
sp. Chlamydomonas
cd
Surfacetreatmentimproveremovalefficiency
25
Cyanobacteria
Zn
Efiicient
Fucas,ascophyllum,
Ni, Pb
Fucus> Ascophyllum> Sargassum
Ulothrix, Spirogyra
Pb,ZN
Efficient
69
Scenedesmus Selenestrum ChloreIIa
Cu,Pb,Cr (III)
67-98%removal
26
Ctiladoptiora crispata
Cr
Eflicient
142
Cyancbacteria
Zn,Mn
An: 10.3mg/g,Mn 10.30mg/g
t34
Oscillatoria sp
Cu,zn,Co
Effrcient
88
FUNGI IN METAL REMEDIATION A wide variety of fungal isolateshave also'been reportedto removeheavymetalsfrom aqueoussolutionas well as certainindustrialeffluent.The metalslike Ag, Cd, io, Cu, Ni, Cr, Pb, Au, ZnEtc., which aretoxic to human being,are treatedwith fungalisolatesin orderto makethe effluentetc. harmlessto aquaticlife, thoughthe rate of removalvary with the typeof theisolateandits metabolic states,Isolateshavealsobeenreportedto removetheseions in viable as well in non- viable conditions.These The rate of are now well characterized. characteristics like pH, depends on several factors is adsorption of biomassand solutes(i.e. metal ions), concentration pretreatmentof biomasspresenceof physicaVchemical etc. variouslegendsandtoxicantsin suspension Aleemlo3reportedgrowth of Rhizopusnigricans, AspergillusandTrichodermat'iridae in a grey soil, Yin et al6astudiedthe removalof Cd from aqueoussolutionby using pretreated fungal biomass cultured fonn starch
t52
136,137
,l4l 72
wastewater, They haveused.a R. oryzae,R. oligosporisand R. arrhizusto removePb, Cu, Cd, Zn from solution.The study. showed that the fungal biomassof R. arrhiz.,ts exhibitedre4sonablyhigh uptake capacitiesfor Cd (upto 0.56 mmoVg,Pb (0.61mmoVg),copper(0.60mmoVgaud Zn (0.53 mmoVg).Using dormantsporesof Neurospora tetrasperma, it hasbeenreportedrrE thatthetestbiosorbent is efficientin removingCu andHg. Azabet al l16cornpared severalfungito removeCd from syntheticsolutionandalso comparedwith activatedcarbon.It was reportedthat the performance of fungal biosorbents was better than conventionaladsorbent, Uptakeof variousmetalions were studiedin detailby variousworkersl0'52'53'65.Usingdead biomassof R. nigricans,Bai andAbrahamr# foundthatthe acid treatment of non- viablebiomassenhance the Cr (VI) removalpropertyof biosorbent.Table4 summarizes certain important types of fungal biosorbentsused by various investigatorsto removecertainheavymetalsfrom solution andeffluents.
MARKA].{DEYCtAI.
FORREMOVALOFHEAVYMETALS TABLE4: FUNGALBIOSORBENTS Reference
Metal
/ comments Efficiency
AgaricusmacrosPorus
of toxicmetals Removal
effrcient
70
Neurosporacrassa
Cr(VI)
removal Significant
75
Mucor hiemalis
Cr(VI)
effective
Aspergillussp
Zn
culture Promising
Rhizopusarrhizus
C(VI), CuandNi
efficient
58,59
Aspergillusniger
Cr,Cu,Ni andZn
effective
83
Mucor hiemalis
Cr (III)
effective
M
Mucor meihi
Cr
L14mmoVg
62
Coprinuscomats CoprinusrarJious
Hg
Micro/g 0.08-7.94
86
Asp.nNiger
ZruCd
> 75Yoremoval
76
Leaf molds
Cr,
2ndorderreaction
55
Mold
Cu,Pb,Cd,,Zn
0.28-0.56m molCd/g
64
RhizopusAsp,sP.
Cd
0.063m moVg
68
sp. Saccharomyces Candidasp.
U, Sr,Se
recovery Effective
tt2
R. arrhizus,
Zn
Rhizopushadshownexcellence
39
Penicillium,Rhizotonia, Trichodermasp.
Zn,Pb
EffectivePb removalthanZn
120
Aspergillussp.
Co
Morphologicalchanges
34
Penicillium IapidosPum
Cr, Hg,Zn,Pb,Al,Ni
Effluent
65
NeurosporatersPrema
Cu,Hg
Goodremoval
ll8
Mucorhiemalis,
Numberof metals
Effectiveremoval
35
R. u'rhiztrs
Cu,Cd,Ni, Co
Effectiveund..onorniral recovery
66
Aspergillus,PenicilIiunt Yeast Streptontyces,
Cu
Ferundichfor Aspergillus Penicillium.,Yeast
82
Aspergillus,Penicilliunt Trichoderma,Phoma,Rhi Candida
Cd,Cr,CuCu,Co,Zn, andFe
46-89%
Fusariuntsoloni
Pb
Efficient
145
viritlae Trichodernra
Cu
80'/6
i0+
Cu,Co,Ni, Cr' Ag,Pb,(-'.d,Zn,
30-99%
51
Organisms
t
48 38
P. chrysogenum S. cerevisiae
A. Oryzae, NerusproasitoPhila, P. chrysogenum
-Aspergillus niger
52-54
us,
153
BIOSORBEN'IS FORREMEDIATION BACTERIA FOR METAL REMEDIATION Considerableamountof work has also beendone to removeheavy metalsby biosorption/bioaccumulation using bacteriavariables71.Suttleworthand Unz lo6have reportedthe growth of filamentousbacteriain ihe presence plantandhave of heavymetalsin activatedsludgetreatmerrt determinedthe effectsof heary metalson the growthof the bacteria.Metalslike Cu, Cd, Zn, Pb, Cr and Ni may be presentin wastewaterandrangesfrom a low of l0 pm to a high of 100 prn. They have determinedthe bacterial requirementfor Cd and the toxicity of heavy metal in ra7 relation the level of other ions. Singh and Chauhan isolatedBacillus subiilts from fly ash and studiedits Cu uptakecapacityin the lab, They foundthat theperformance of mutantstrainwasmuchhigherthanthewild strains. Using dry biomassof Mycobacteriumsmegmatis, la8 Texier et al. studiesthe selectivebiosorptionof lanthanide(La, Eu) ions. They obsen'edthat the test biosorbentprel-erentially adsorbEu3*with respectto La cationsand in both the process,follow the Freundlichand 23 Langmuir relations.Chang et al. selectedbiomass aentginosaPrJPseudomonas 2l for biosorption studiesfor thattherestingcellswereabie Cu, Cd andPb andobserved to uptakeup to I l0 mg Pb/g dry cell and the inactivated cellscanequallyefficientin adsorption andrecovery.Using E. coli,Xie et al33foundthatthetreatment of biomasswith SodiumChloroaceticacid enhancemetalbindingcapacity for Au3*,cd2o.co2*.cr3', cu2*,Hg2*,Ni2*,pb2*.se2*,s/'' v2*, zn2*, Asoz, cro42-, Mno4t- and wo42 ions from aqueousphase. Selectiveelution conditionsrvere also to allowtherecoveryof individualmetalfrom demonstrated mixture of metals.Gopalanand Veeramani7a isolated Aeromonas.q,p. thatwasfoundcapableof removing68 % Fe from syntheticferric citratemedium.The maximumiron rernovalefficiencyof 99.6o/owasobtainedat 72 h retention time with specificiron removedrate of 9.5 mg/g/h.The cultureThiobacillus ferrooxidansrvasisclatedby Pathaket lae al and found that the isolatehas higheraccumulation effrciency for Fe, Pb and Cu. In another similar Xie et al. " *.r. ableto removeAu, Cd, Co, experiments, Cr, Cu, Hg, Ni, Pb, Se, Sr, V, Zn etc. from synthetic 43 have evaluatedvarious solution. Grapelli et al. Arthrobuctersp. for Cd decontamination of liquid stream. Their findingshaveconfirmedwhathasbeenhypothesized possibilityof usingmetal concerning by otherresearchers tolerant bacteriaalternativefor treatmentof industrial effluent. Bosecker2T hasinvestrgated the applicabilityof the microbialbasedtreatmenttechnologyfor metal recovery from non-sulfide industrialpfproducts like slag,galvanic sludge, filter pressresidue, filter dust,fly ashetc. from someproducts, Cu,Cr, , Zn, Y werecornpletely removedby thioxidans Thiabacillus thatcouldrerloveup to 6.6 e Cu./L
t54
{ .* :.i ,, 6.3 g YlL,24.4 g ZnlL. or 21.0 g CrlL in the leaching medium. In principal, bacterial metal recovery tom industrialeffluentseemsto be feasibleand may contnlbute to an increasein suppliesof raw material as well as to detoxificationof industrial effluent resulting in reduced environmentalpollution problem. Ebner e8 has used different speciesof Thiobacilh.rs for leachingof sulphidic dustandoxidic fly ashfrom a Cu process,slag,from a lead smeltingprocessand Jarositefrom zinc electrolysis.The leachingefficiency was specific to materialfor treatment and inoculatedbacterialspecies.The maximumoutputfor Zn was around95% and around70% for copper.Table5 summarizes s()nreimportantbacterialsp.,usedby various workersfor rcurovalof various metalsform the aqueous state. ACTINOMYCETES BIOREMEDIATION
AND
YEASTS
FOR
Similar to fungal and bacterialisolates,a wide variety of actinomycetes and yeastswere also studiedby various investigators(Table 6) to removethe metal ions from aquatic environment. U singScccharomyces cer evisi ae, efforts have been made to removeCd, Th, Cu, etc..by 28'4t' 42'6't'e0't2t''22. variousinvestigators Thesereports indicatethe biosorptioncapacitybetween2.4-71mglgfor Cd,1.9-2.5 mg/gfor Cu, 100-125 mg/gfor Th,33-155mg/g for U. In anothersimilar experiments, Brady et al. 26 prepared a biosorbent by treatingyeastwith hotalkali.They observed thatthebiosorbent wascapableof accumulating a widevarietyof cationslike Fe, Cr, Hg, Pb,Cd, Co,Ag, Ni etc.from syntheticsolution.Thealsofound> 99%removed of Zn, Cr, Cu form electroplating effluentand around5060% Cr from tannery effluent. Using equi-molar concentration of Cd and Zn, Ting and Teo 37studiedthat presence of co- ion did not appreciablyaffect the instantaneous uptakeof othermetalthat indicatesthatthese ionsmaybe boundon diflerentsiteson thecell wall of test organisp.ln our earlierinvestigation at initialconcentration_ of 50 mg/L of individualmetal(s)in syntheticsolution, Cqndidu tropicalis rvas able to remove Crt, (79%) Cd (79%),Cr (75%) andZn (63%)frommultimetallic solution' 52-54
IMN,IOBILISBD BTOREMEDIATION
BIOSORBENTS
FOR
The efficiency of microorganisms as rvell as preparedfronr non-viablebiomasses biosorbents could be irnprovedby immobilizingthe sameby someentrapping agentslike alginates, polyacrylamide,silicaget etc.As an alginates,use of sodium alginates,calcium chloride, barium-andstrontiumchloride is quite common, It is becausethe calcium helps in stabilization, while Ba maintainsstabilityand providesnecessary rigidity and Sr permeability makesadequate to immobisates. When
MARKANDEY etsl. BY BACTERIA TABLE5:METALBIOSORPTION Bacteria
Metal
bacteria sulfate-reducing immobilizedbacterial biomass baumannil,. Acinetobacter Pseudomonas aeruginosa nasaeruginosa Pseudomo Rhodotorulq mucilaginosa Bacillussp. nas aeruginosa Pseudomo Desulftvibriovulgaris Ps.aeruginosa Thiobacillusferr oxidans
Znprecipitation Cu
Efficiency,Remark phosphogypsum asa sulfate effective
Ni
industrialwastewater, effective
Ps.Aeruginosa SPAeromonas Mixed microbes E coli Ps.aeruginosa Mycobacter ium smegmatis Bacillussubtilis Ps.flurescens ArthrobactersP. ThiobcillussP. Thiobacillusfe r rooxidans DesulfovibriosP. Pseudomonas
:
inactivatedcells,effective effrcient Effeitive adsorptionby spores andcomparisonstudies characterization biomass palladized Surfacecharacterization soil,Zn (57 !32%),Mt Contaminated (57!28%(C:u(49!r3%) NADH dependent Cr(VI) 0 cultivation,99% 27-29 C, Chemostat Fe mg/lt. removal,initial650 RBC,steadystate98%fiom initial 100-200 Cr mg/lt. Au,Cd,Cr,Cu,Hg,Ni, Pb, Chemicallytreatedanduntreatedbiomass, efhcient Se,Sr Restingcells,82-98%removal Cu,Pb,Cd highertemp.reducedremovalefhciency La,Eu wild andmutantstrainefficient Cu NTA duringandaftergrowth,accumulation Cd,C.u,Zn for elution50-90%removal Goodremoval Cd Efficientculture Cu,Pb,Zn removal Economical Fe Effectivecultures U Effectivecultures Co
Hg Ag freeandcomplexed Cu U Cr(VI)Reduction Cr(III)andCr(VI) Zn,Cu,Mn
a l J I
23 73 l5l 106 107 7l 44 5/.
74 22 JJ
20 148 36 85 +J
98 27 119 94
TABLE6:ACTINOMYCETESANDYEASTSFORREMEDIATIONOFHEAVYMETALS Organism
Metal
Efficiency,Comment
cerevisiae SaccharomYces
Pb
cerevisiae. Sacchromyces Baker'syeast cerevisiae Saccharomyces
Cd,CU Ni Varietyof heavY metais U Cd Cd Cd
Equilibriumandmechanism analysis etTective
Ior S. cerevisiae,Sporobiolomyces salmi on[c'o S. cerevisiae S. cerevisiae S. cerevisiae S. cerevisiae S. cerevisiae S. cerevisiae S. cerevisiae S. cerevisiae
t t
Th Cu Variousnietals C,ZN
155
efl'ective goodscavenger ngls 2.4-31.2 8.9mg.g 7l mglg mgig 33-l-50 1 1 9m g i g 1.9mglg > 99%An, Cr, Cu fromelectro plating,50-60%Cr Fromtannery Noninteractionbetweenc
Reference
77 40 47 89 67 28 121 90 6 7, 1 2 2 42 4l 26 an ) l
BIOSORBENTS FORREMEDIATION 150. euymes are qsed,it has severaladvantages Theseare 'indicating the successfuluse of these several reports entrappers in decontaminationprocess with effrcient regenerationand prolongedfunction over a considerable periodof exposureto8. Rai and Mirllick'7 have adopted alginate immobilized and free cells of Anabaenadoliolum and Chlorellavulgaris for removalof Cu and Fe. They noticed that the immobilization offers protection against metal toxicity and concluded that immobilized cells 'are heavymeals appropriate-and effectite toolsfor scavenging form the conkminatedaqueoussystem.Similarly, Rome rr2 have used immobilizedbiomassof ^S. and Gadd cerevisiaefor removalof certainheavy metalsand radionuclidesin batch- and continuousmode.They found that since the processis biphasic,surfacebiosorptionbeing r5r followed by energydependentin flux. Leuis and kiff haveusedan immobilizedfungalbiomassfor theremovalof heavymetalsfrom solutionand tried support/ entrapperof immobilization and found that entrapped biosorbents phases. effrcientlyremovemetalsionsfrom aqu€ous RECOVERY OF BIOSORBENTS
METALS
FROM
LOADED
FACTORSAFFECTING Th; BIOSORPTION
Once the biosorbentsexposedto the metallic contaminants, the later get removedfrom the environment. This biphasicsystemhas industrialapplication.Generally recoveryof heavymetalsfrom loadedbiomassis performed by- elutriation -
acidification
-
rgplacement by otherionsand,
-
treatmentrvith complexantse.g. EDTA, NTA, DTRA etc.
powder and Cd depletedelectrolyte,which is recycledas eluent.The Cr (VI) of tanneryeffluent,which was loaded on Mucor meihi was also recovered 100% when the 62. acid/basetreatmentswereperformed Fallaet al. 85haveusedNTA, EDTA,DTPAetc.as efuting agentsto recovermetal ions like Cd, Cu and Zn from the metabolicallyactive biomassof Ps.fluorescens. They observedthatusingNTA, around90%of accumulated metals of the after growth experimentswas possibleto recover,but onlly 50% of that accumulatedduring the growth. {-isingvarious concentrationof hydrochloricacid, thiourea m citrate, ammonia, nitrolo triacetic acid and ethylenediamine tetra acetic acids elution conditionsto allow the recovery of individual metals from mixture, howeverthe chosenmethodofrecoverydependon the ease of metal removalor the bir:massas a reusablematerial.If the wastebiomassis cheap,the recoveryby incinerationor acid/alkalidissolutionmay be economically feasiblerr3.If microbes and metals are equally important then nondestructiverecoveryis useful. Loadedbiomasselutedwith strongacid or pyrometallurgicaltreatmentandbiomasscan ?6. berecycled
Usingthe principle,a systemhasbeendeveloped recoveryof U from solutionusingRhizopus for continuous The loadedbiomasswaselutedby alkali arrhizusbiornass. solutionand the adsorbbdmetals ions were recovered. A Advantageof this processwas to reusesthe biosorbent. hasbeendeveloped commercialapplicationof biorecovery by Advanced Mineral Technology,Known as AMTfonn an non- viablebiosorbent Bioclaimusesa granulated The granuleshave a high unpublishedmicroorganism. capacityfor metalions and can be ernployedin the fixed hasfound bedcanisters or fluidizedbedreactor.Theprocess a commercialvaluein the removalof Au form colnposited sample of goldcyanide solutioner. process by Butter A multistage hasbeendeveloped e8 et al to relnoveand recoverCd from syntheticsolution. The loaded biosorbentwas eluted using an electrolyte solutionand the metal was recoveredfrom the elute by using a rotatingcathodecell, resultingin Cd electrolysis
r56
The following factors affect the biosorption process: 1.. Biosorptionis mainly usedto treatwastewater where morethanonetypeof metalionswouldbe present; the removalof one metal ion may be influencedby the presence of othermetalions.For example: U uptakeby biomassof bacteria,fungi and yeastswasnot affected by the presenceof Mn, Co Cu, Cd, Hg and Pb in 152. solution In contrast,the presence of Fe2*andZn2* was found to influence uraniumuptakeby Rhizopus arrhizus35and Co uptakeby differentmicroorganisms seemed to be completely inhibitedby thepresence of U, Pb;Hg andCur52. 2. Biomassconcentration in solutionseemsto influence the specific uptake: for lorver values of biomase concentrations there is an increasein the specific uptake.Gadcl,et al. a2suggested that an increasein biomassconcentration leadsto interference between the binding sites. lrourestand Roux ee invalidatedthis hlpothesisattributingthe responsibility of thespecific uptake deoreaseto metal concentration shortagein solution.Ilence this factor needsto be taken into consideration in anyapplication of microbialbiomass. 3. ThepH seemsto be themostirnportant parameter in the biosorptivepro-Qess: it affects the chemistryof the metals,the activityof functionalgroupsin thebiomass andthecompetition of metallicionsr5r.
MARKANDEYet al revealsthat not all metal-pollutedwastewatergeneratmg industrieshave the interestor o-apahilityto heat-efruents' Thus, most of the industriesopt for just basictreatrnentto comply with the legalities. The optimum pH and conditionsfor both the growthandheavymetal temperature for eachisolate. removalweredetermined
4. Temperature seems not to influence biosorption r54. in therangeof20-350C perfonnances CONCLUSION Contaminationof aquatic resourcesby a large variety of heavy metals is now consideredas a major environmental hazard. Their conshntly increasing concentrationshave become more noticeable after an intensive industrial development. The environmental resources,which are close to the industrialvicinities, are more susceptibleto the contaminationto thesehazardous pollutants.Heavymetalsare the majorcausesof pollution as it poseserioushealthhazardto flora ofaquatic resources metals persist indefinitely in tlte These and fauna. environmentand overtax self purification capacityof the To biosphereand limits the life activityin the ecosystem' handle such problem, the suitability of adsorbentsof microbiologicalorigin has emergedin the last few decades as one of the most promisingalternativesto conventional strategies' heavymetalsmanagement Many types of yeast,fungi, algae' bacteriahave been reportedto have the capacityto concentratemetals theminside solutionsandto accumulate fromdiluteaqueous can ecosystem the cell structure.Besides, microbial drasticallyalterthe fateof the metalenteringinto aquaticor soil environments.These microbes alter the form of occulrence of metal through methylation, chelation, complexation,catalysisor adsorptionetc. affectingtheir in thefoodchain. andmovement bio-availability The use of microorganismsand the material preparedby themfor removaland recoveryof heavymeals due to their excellentperformance' has gainedimportance reproducibilityand low cost. Microorganismsexhibit metalbindingcapacityin viable-asrvell as noninteresting beenfound to viable state.Certainmicroorganisms,have like Ag, Cd, metals large quantitiesof heavy accumulate Co, Cu,Ni, Pb, Zn,Cr etc.from solutionandmetalbearing effluent.The microbesand microbialproductsare highly of theseionsandthisuniquequality efficientaccumulators but alsohelpto recover not only detoxifytheenvironment, etc' The radionuclides nretals, precious important certain inexpensive produced using be can easily biosorbents growth media or obtainedas a byproductfrom some catralsoout industry.The judiciouschoicecf biosorbent rvhichhave resins exchange ion commercial competethe metai(s)' of the removal conventionallybeen used itt of the However,thereis a needto havemore knorvledge and better develop to in order involved basicmechanisms remains question that still The mqor effectivebiosorbents. are effective. to be answeredis that althoughthe sorbetrts envirorunental anrJ is sorrnd teciurology the underlying is growingvery fast, still biosorptionis not a awareness treatmenttechnology'Criticalanaiysis popularwastervater
To attract more usageof biosorbenttechnology, certain strategieshave to be formulatedto centralizethe facilities for acceptingthe used biosorbentwhere further the processingof the biosorbentcan be doneto regenerate usable into metal recovered the biomassand then convert approach form. This will furtherrequirean interdisciplinary with integrationof metallurgicalskills alongwith sorption treatmentto developbiosorptiontechnology and wastewater for combatinghealy metalpollution in aqueoussolutions. Suchremediationsystemshavebeenprovedeconomicaland provides eco-friendly alternative over conventional treatmentsystem.The informationavailableis limited to few metalions removalsby the specializedmicrofloraand are confinedto laboratoryscale most of the investigations with some studieswith syntheticsolutionandin few cases, More feasibleaswell asreliable dilutedindustrialeffluents. information is required for a better understandingand effective and economicaluse of thesesvariablesfor remediationof metalbearingeffluentsfor field application. The eluentsare usedfor recoveryof metalsform loaded and much assessment biomassalso needscomprehensive in the microbes information is required to apply multimetallicsystemfor selectiverecoveryof metalsfrom waysto restorethe loadedbiomassin the mosteconomical environment. of theaquatic wholesomeness REFERBNCES
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