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Biosorption of Cr(VI) onto marine Aspergillus niger : experimental studies and pseudo-second order kinetics

The removal of hexavalent chromium from aqueous solution was studied in batch experiments using dead biomass of three different species of marine Aspergillus after alkali treatment. All the cultures exhibited potential to remove Cr(VI), out of which,
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  ORIGINAL PAPER Biosorption of Cr(VI) onto marine  Aspergillus niger : experimentalstudies and pseudo-second order kinetics Yasmin Khambhaty   Kalpana Mody   Shaik Basha   Bhavanath Jha Received: 7 January 2009/Accepted: 19 March 2009/Published online: 3 April 2009   Springer Science+Business Media B.V. 2009 Abstract  The removal of hexavalent chromium fromaqueous solution was studied in batch experiments usingdead biomass of three different species of marine  Asper-gillus  after alkali treatment. All the cultures exhibitedpotential to remove Cr(VI), out of which,  Aspergillus niger  was found to be the most promising one. This culture wasfurther studied employing variation in pH, temperature,metal ion concentration and biomass concentration with aview to understand the effect of these parameters on bio-sorption of Cr(VI). Higher biosorption percentage wasevidenced at lower initial concentration of Cr(VI) ion,while the sorption capacity of the biomass increased withrising concentration of ions. Biomass as low as 0.8 g l - 1 could biosorb 95% Cr(VI) ions within 2,880 min from anaqueous solution of 400 mg l - 1 Cr(VI) concentration.Optimum pH and temperature for Cr(VI) biosorption were2.0 and 50  C, respectively. Kinetic studies based on pseudosecond order models like Sobkowsk and Czerwinski,Ritchie, Blanchard and Ho and Mckay rate expressionshave also been carried out. The nature of the possible cell–metal ion interactions was evaluated by FTIR, SEM andEDAX analysis. Keywords  Aspergillus niger     Biosorption   Hexavalent chromium    Kinetics    Marine fungi Abbreviations C  i  Initial metal concentration (mg l - 1 ) C  e  Equilibrium concentration (mg l - 1 ) k   Sobkowsk and Czerwinski as well as Ritchie kineticrate constant (min - 1 ) k   Ho’s Pseudo-second order and Blanchard kineticrate constant (g mg - 1 min - 1 ) q i  Observed sorption capacity of batch experiment  iq e  Equilibrium sorption capacity (mg g - 1 ) q t   Sorption capacity at time  t   (mg g - 1 ) Q i  Estimated sorption capacity of batch experiment  i R 2 Regression coefficientSE Standard errorSSE Sum of squares error t   Biosorption time (min) V   Volume of metal solution (l) W   Mass of sorbent (g) a  Blanchard kinetic model constant Introduction The unabated discharge of effluents by diverse industriesconstitutes one of the major causes of land and waterpollution by chromium compounds and has become anobnoxious health hazard (Barnhart 1997). Out of hexava- lent and trivalent species of chromium which are prevalentin industrial waste solutions, the hexavalent form has beenconsidered more hazardous to public health due to itsmutagenic and carcinogenic properties. Cr(VI) causessevere diarrhea, ulcers, eye and skin irritation, kidneydysfunction and probably lung carcinoma (Gupta et al.2001; Costa 2003). Conventional physical and chemical methods for the removal of Cr(VI) from wastewaters,including ion-exchange resins, reverse osmosis, reductionand precipitation and coagulation, are highly expensive andalso ineffective at lower concentration of metal ions. Y. Khambhaty    K. Mody ( & )    S. Basha    B. JhaDiscipline of Marine Biotechnology & Ecology, Central Salt &Marine Chemicals Research Institute, (Council of Industrial andScientific Research), Bhavnagar, Gujarat 364002, Indiae-mail:  1 3 World J Microbiol Biotechnol (2009) 25:1413–1421DOI 10.1007/s11274-009-0028-0  Moreover, these methods also generate large quantity of toxic sludge (Bai and Abraham 2001). The US EPA has set the discharge limit of Cr(VI) to surface water below0.05 mg l - 1 while the total Cr including Cr(III), Cr(VI)and its other forms to below 2 mg l - 1 (Baral and Engelken2002). Consequently, it is crucial to develop new envi-ronmentally friendly methods which are sensitive, effectiveand commercially viable.Biosorption of heavy metals by biomaterials has beensuggested as a potential alternative to the existing physi-cochemical technologies for detoxification and recovery of toxic and valuable metals from wastewaters. It employs theuse of divergent biomass such as seaweed (Yun et al.2001), microalgae (Gupta et al. 2001), fungi (Sag and Kutsal 2002), bacteria (Nourbakhsh et al. 2002) and vari- ous other plant materials (Sharma and Forster 1993; Raji and Anirudhan 1998; Gardea-Torresdey et al. 2000). Fun- gal biomass enjoys advantage over other biomass as it canbe economically and easily procured in substantial quan-tities, as a byproduct from industrial fermentationprocesses. Furthermore, since such abundant dead fungalbiomass is of little use, it has been identified as a potentialsource of biomaterial for the removal of chromium fromwastewaters (Park et al. 2005a). In the absence of adequate reports available on bio-sorption of metals using marine fungi, detailed studies needto be conducted before confirming their similar applica-tions. Babich and Stotzky revealed that the growth of somemarine fungi exposed to nickel was less depressed in thepresence of magnesium compared to their growth in thepresence of nickel alone (Babich and Stotzky 1983). Hicks and Newell found that exposing  Phaeospharia typharum , asalt marsh fungus, to mercury at metal concentration of 0.74 mg/l resulted in no significant change in glucosaminecontent or growth as compared to the cultures grown in theabsence of mercury (Hicks and Newell 1984). Taboski et al. (2005) discovered the effect of lead and cadmium on the growth of two species of marine fungi,  Corolosporalacera  and  Monodictys pelagic . A major advantage of biosorption is that it can be used in situ, and with properdesign, may not need any industrial process operations andcan be integrated with many systems in the most eco-friendly manner. The present study explored the use of dead fungal biomass for the treatment of industrial efflu-ents. Further, all the industries discharge their effluents inthe marine environment which generate stressful conditionfor living organisms. Fungi which could grow under suchstress conditions are acclimatized to these constraints andhence they are congruent for biodetoxification of heavymetals from industrial effluents. Considering these points,in the present investigation, three different dead marinefungal biomass were screened as biosorbents for theelimination of Cr(VI). Various parameters such as contacttime, pH, initial Cr(VI) concentration, biomass concentra-tion and temperature influencing Cr(VI) biosorption wereexhaustively studied. In the present study, four differenttypes of pseudo second order expressions were also used torepresent the kinetics of Cr(VI) onto  A. niger  . The nature of the possible cell–metal ions interactions was also evaluatedby FTIR, SEM and EDAX analysis. Materials and methods Collection of samples and isolation of fungiSeawater and sediment samples collected in sterile con-tainers along the Gujarat coast (West coast of India) werebrought to the laboratory. These samples were inoculatedon potato dextrose agar medium containing (g l - 1 seawa-ter) boiled and mashed potato 500 g; dextrose 20 g; agar30 g and incubated at 30  ±  2  C. The fungi were purifiedon the same medium. The cultures were routinely main-tained at 4  C on potato dextrose agar slants. The isolatedfungi were identified at the Aghakar Research Institute,Pune, India.Preparation of dead fungal biomassThree different species of   Aspergillus  were chosen as testfungi i.e.  Aspergillus niger  ,  Aspergillus wentii  and  Asper-gillus terreus . These were cultivated in the mediumcontaining (g l - 1 of seawater) boiled and mashed potato250 g and dextrose 20 g and incubated at 30  ±  2  C. After7 days of incubation, the live fungi were killed by boilingin 0.5 N NaOH solution for 15 min and then washed withgenerous amounts of deionized water till the pH of thewash solution was in the neutral range of 7.0–7.2. Afterwashing, the biomass was dehydrated at 50  C for 24 h andpowdered. The dried biomass was stored in a desiccatorand used for subsequent experiments.Cr(VI) removal experimentsAll the experiments (except the experiment on the effect of temperature) were conducted at a constant temperature of 35  ±  2  C to be representative of environmentally relevantconditions. 2.828 g of K  2 Cr 2 O 7  was dissolved in 1 l of distilled water to obtain a stock solution having1,000 mg l - 1 of Cr(VI). The stock solution was thendiluted to obtain test solutions of desired strength. Inexperiments to screen efficient fungal species, 2 g l - 1 of dead biomass of each fungi was mixed with a solutioncontaining 10 mg l - 1 of Cr(VI) separately at pH 2.0 at35  ±  2  C for different time intervals. The most promising 1414 World J Microbiol Biotechnol (2009) 25:1413–1421  1 3  fungus was further used for optimization of conditions. Inorder to find the effect of Cr(VI) concentration on bio-sorption, solutions containing 10, 25, 50, 75, 100, 150, 200,250, 300, 350 and 400 mg l - 1 of chromium were used.Effect of temperature on the biosorption of Cr(VI) wasstudied using three different temperatures viz. 22, 37 and50  C for incubation with different concentration of chro-mium such as 25, 50, 75, 100, 150, 200, 225, 250, 275, 300,325, 350 and 400 mg l - 1 . The effect of pH was observedby varying the pH of the metal solution i.e. 1, 2, 3, 4 and 5where the pH of the solution was achieved at the desiredvalue using 0.1 N HCl or 1 N NaOH. The effect of biomassconcentration on the Cr(VI) removal was studied employ-ing 0.8, 2.4, 4.0 and 5.6 g l - 1 of biomass. The flasks wereagitated on a shaker at 180 rpm. The solution was sampledat regular intervals, filtered and the Cr(VI) concentration of the filtrate was analyzed.Kinetic experiments were conducted with 25 ml of 250 mg l - 1 Cr(VI) solution at pH 2.0 and 35  ±  2  C andsamples were drawn at regular time intervals. The pH of the solution was monitored constantly with a pH electrodeand adjusted with HCl or NaOH solution, if deviationswere observed.All the biosorption experiments were repeated twice toascertain the results. The data were the mean values of two replicate determinations. In order to check thereproducibility of the results, random tests were madeunder different experimental conditions. Cr(VI) experi-ments were reproducible to within, at most, a 3% error.Control experiments, processed without the addition of biosorbent, confirmed that the sorption of metals on thewalls of glass flasks or in the filtration systems wasinsignificant.Chromium analysis and uptake capacityCr(VI) was analyzed spectrophotometrically after com-plexation of metal ion with 1,5-diphenylcarbazide.Absorbance was recorded at 540 nm, using Shimadzu (UV-1201, UV–VIS) spectrophotometer using standard method(Clesceri et al. 1998).The amount of Cr(VI) biosorbed at equilibrium,  q e (mg g - 1 ), which represents the metal uptake, was calcu-lated from the difference in metal concentration in theaqueous phase before and after biosorption, according tothe following equation: q e  ¼  V  ð C  i    C  e Þ W   ð 1 Þ where  V   is the volume of Cr(VI) solution (l),  C  i  and  C  e  arethe initial and equilibrium concentration of Cr(VI) insolution (mg l - 1 ), respectively, and W is the mass of drybiosorbent (g).FTIR, SEM and EDAX studiesInfrared spectra of unloaded and Cr(VI) loaded biomass of   A. niger   was obtained using a Fourier Transform InfraredSpectrometer (FTIR GX 2000, Perkin-Elmer). For theFTIR study, 30 mg of finely ground biomass was palletedwith 300 mg of KBr (Sigma) in order to prepare translu-cent sample disks.The surface structure of biosorbent was analyzed byscanning electron microscopy (SEM) coupled with energydispersive X-ray analysis (EDAX) using LEO 1430 VP.Unloaded and metal-loaded  A. niger   biomass samples weremounted on aluminum stab sequenced by coating with athin layer of gold under vacuum to increase the electronconduction and to improve the quality of the micrographs. Results and discussion Screening of different fungal species for Cr(VI)removalIn order to screen the efficient fungal species for Cr(VI)removal, time dependent concentration of Cr(VI) wasmeasured in a batch system containing three different spe-cies of   Aspergillus . Evidently, the initial removal rate of Cr(VI) depended on the species of   Aspergillus ; thesequential order was  A. niger  [  A. wentii [  A. terreus (Figure not shown). The objective of the screening experi-ment was to recognize potential fungal species havingmaximum biosorption capacity with respect to Cr(VI). Thiswas exhibited by  A. niger   where 96.7  ±  1.284% of Cr(VI)was biosorbed within 1,440 min as compared to84.8  ±  0.927 and 55.3  ±  0.596% by  A. wentii  and  A. ter-reus , respectively. Based on these results,  A. niger   was usedfor additional studies. It was also observed that in all thefungi studied, 40–65% biosorption of Cr(VI) was observedwithin the first 120 min which incrementally increased withtime.Effect of initial concentration of Cr(VI) on its sorptionThe initial concentration of Cr(VI) in the solution extraor-dinarily influenced the sorption rate of Cr(VI). It was notedthat as the initial concentration increased, the sorption of Cr(VI) too correspondingly increased as it is generallyexpected due to equilibrium process. When the initial con-centration of Cr(VI) increased from 10 to 400 mg l - 1 , thesorption capacity increased from 2.5  ±  0.05 to54.16  ±  0.582 mg g - 1 of biomass at 30  ±  2  C within2,880 min (Fig. 1) at pH 2.0 (regression coefficient, r  2 =  0.962). The increase in sorption capacity of sorbentwith the increase of Cr(VI) ion concentration is consequent World J Microbiol Biotechnol (2009) 25:1413–1421 1415  1 3  to higher availability of Cr(VI) ions in the solution. More-over, higher initial concentration provides increasedpropelling force to overcome all mass transfer resistance of metalions betweentheaqueousandsolidphasesresultinginhigher probability of collision between Cr(VI) ions andsorbents. This also results in higher metal sorption capacity.Simultaneously, the percentage biosorption of Cr(VI) ionwas decreased as the initial concentration was increasedfrom10to400 g l - 1 (Fig. 1; r  2 =  0.984).Thismightbedueto the lack of available binding sites in the biomass and theconsequent increase in the number of ions competing for thebinding sites. Analogous results have been reported by Baiand Abraham for Cr(VI) biosorption by  Rhizopus nigricans wherepercentbiosorptiondecreasedwithanimprovementinCr(VI) concentration (Bai and Abraham 2001). Similarly,Parketal.observedthat  A. niger  couldbiosorb100%Cr(VI)at 200 mg/l concentration within about 24,000 min (Park et al. 2005a) whereas in the present investigation 100%biosorption was observed at 100 mg l - 1 of Cr(VI) concen-tration within about 2,880 min.Evaluation of kinetic parametersThe Cr(VI) sorption capacity at 250 mg l - 1 Cr(VI) con-centration versus time was examined at biomass dosage of 4 g l - 1 and pH 2.0 (Fig. 2). At 100 mg l - 1 of initial Cr(VI)concentration, Cr(VI) was completely eradicated in1,440 min of contact time. Park et al. (2005b) observed that contact time required for the complete elimination of Cr(VI) varied from 1,020 to 10,200 min depending on thesolution pH. Higher contact time may be due to thedepletion of the protons participating in the reduction of Cr(VI) (Park et al. 2005a). Various pseudo-second order kinetic models like Ritchie(1977), Sobkowsk and Czerwinski (1974), Blanachard et al. (1984) and Ho and McKay (2000) have been used in modeling the kinetic data (Table 1). The kinetic parameterswere evaluated by non-linear regression using DATAFIT  software (Oakdale Engineering, USA). The calculatedkinetic rate constants and their corresponding coefficient of determinations  R 2 , standard error (SE) and sum of squareserror (SSE) are presented in Table 2. The smaller SE andSSE value denotes the better curve fitting. From Table 2, itcould be observed that the second order models of Ritchieand Sobkowsk and Czerwinski’s transforms to a similarnon-linear expression. This suggested that both Ritchie andSobkowsk and Czerwinski shared the same idea on pseudo-second order expression. Likewise, the second orderexpressions of Blanchard et al. and Ho and Mckay trans-form to a same non-linear expression. This confirms thatBlanchard et al. and Ho and Mckay have similar idea onthe pseudo-second order expression. However, Blanchardet al. proposed their model for an ion exchange mechanism,whereas Ho and Mckay’s pseudo-second order expressionwas derived assuming chemisorption and monolayerexposure. Recently, Azizian derived the pseudo-secondorder expression in a more tangible way supporting thetheoretical assumption of Ho and Mckay’s pseudo-secondorder model (Azizian 2004). Fig. 2 shows the experimental kinetic data and the predicted kinetics of Ritchie, 02040608010012010 25 50 75 100 150 200 250 300 350 400 Cr(VI) concentration (mgl -1 )    C  r   (   V   I   )   b   i  o  s  o  r   b  e   d   (      %    ) 0102030405060    C  r   (   V   I   )   b   i  o  s  o  r   b  e   d   (  m  g  g   -   1    ) Fig. 1  Sorption capacity ( d ) and percent biosorption ( j ) at varyinginitial concentration of Cr(VI) ion (pH 2.0, contact time: 2,880 min,biomass dose: 4 g l - 1 ) by  Aspergillus niger  01020304050600 300 600 900 1200 1500 1800 2100 Time (min)   q    t    (  m  g  g   -   1    ) ExperimentalSobkowsk and Czerwinski Ritchie BlachardHo and Mckay Fig. 2  Sorption kinetics for Cr(VI) onto  Aspergillus niger   by non-linear regression method Table 1  Various Pseudo-second-order kinetic modelsModels EquationSobkowsk and Czerwinski  q t   ¼  q e kt kt  þ 1 Ritchie  q t   ¼  q e kt kt  þ 1 Blanchard et al.  q t   ¼ q e kt  þ a q e  1 kt  þ a when  a  =  1/  q e , thenBlanchard model simplifies to q t   ¼  q 2e kt  1 þ kq e t  Ho and McKay  q t   ¼  q 2e kt  1 þ kq e t  1416 World J Microbiol Biotechnol (2009) 25:1413–1421  1 3  Sobkowsk and Czerwinski, Blanchard et al. and Ho andMckay pseudo-second order model by non-linear method.From Fig. 2, as expected, it was observed that the predictedRitchie and Sobkowsk and Czerwinski’s kinetics exactlyoverlapped with same coefficient of determination values(Table 2). Similarly the Ho and Mckay’s pseudo-secondorder kinetics exactly overlapped the Blanchard et al.kinetics with the same coefficient of determination,  R 2 .Table 2 also reveals the calculated rate constant  k  , pre-dicted  q e  by Blanchard et al., and Ho and Mckay pseudo-second order expression. In addition, relatively higher  R 2 and low SE and SSE values (Table 2) of Ho and Mckayand Blanchard et al. kinetics as compared to that of Ritchieand Sobkowsk and Czerwinski’s kinetics corroborates Hoand Mckay and Blanchard et al. second order expression asthe apt expression to represent the kinetics of Cr(VI) onto  A. niger  . Moreover, the predicted  q e  values by these modelsare comparable to experimental value.Effect of temperatureTemperature plays a critical role in the biosorption of metalions. Therefore, experiments were performed to examinethe temperature dependency of Cr(VI) sorption by the deadfungal biomass of marine  A. niger  . The increase in tem-perature vastly improved the Cr(VI) biosorption rate anddecreased the contact time required for complete Cr(VI)removal. Maximum Cr(VI) binding was observed at 50  C(Figure not shown;  r  2 =  0.989). It was evidenced that at avery low initial Cr(VI) concentrations i.e. up to about75 mg l - 1 , temperature did not have significant effect;however, with an increase in initial Cr(VI) concentration,increase in temperature exhibited positive influence on thesorption capacity. It is reported that in cases where theinteraction between metal ions and microbial cell wall isendothermic, higher temperature would enhance bindingwhereas the exothermic interaction would encouragebinding at lower temperature. Bai and Abraham havereported a decline in Cr(VI) sorption capacity at tempera-tures as high as 50  C by  Rhizopus nigricans  (Bai andAbraham 2001). In the present investigation, lowertemperature reduces biosorption and hence the process of Cr(VI) biosorption is concluded to be an endothermicreaction. In general, the increase of temperature induces therate of a redox reaction. Similar results have been reportedwhile working with  Mucor hiemalis  where an increasedsorption rate of Cr(VI) ions have been revealed at tem-peratures as high as 50  C (Tewari et al. 2005). Srivastavaand Thakur (2006) have observed that 30  C was the idealcondition for the bioaccumulation of chromium by  Asper-gillus  sp. Mungasavalli et al. (2007) reported sorptioncapacities of pretreated biomass of   A. niger   for Cr(VI) were14.5, 15.2, 10.6, and 11.6 mg g - 1 at 5  ±  2, 15  ±  2,22  ±  2, and 30  ±  2  C, respectively.Effect of pH of solution on Cr(VI) sorptionEarlier studies on heavy metal biosorption have showedthat pH is an important parameter affecting the biosorptionprocess (Gupta et al. 2001; Park et al. 2005a, b). The experimental results indicated that biosorbtion capacity of dead biomass of   A. niger   improved with an increase inacidity up to pH 1.0. The sorption capacity of Cr(VI) wasreduced from 104.99  ±  2.1483 to 15.49  ±  0.263 mg g - 1 of biomass when the pH of the solution was increased frompH 1.0 to 5.0 (Figure not shown;  r  2 =  0.973). The pHdependence of metal biosorption can largely be related totype and ionic state of these functional groups and also onthe metal chemistry in solution (Park et al. 2005b). Cr(VI) and some other metals such as arsenic, depending on thepH, are known to exist as anions. At low pH values, cellwall ligands are protonated and compete significantly withmetal binding. With increasing pH, more ligands such asamino and carboxyl groups, would be exposed leading toattraction between these negative charges and the metalsand hence increases in biosorption on to the cell surface(Kapoor et al. 1999). As the pH increased further, the overall surface charge on the cells could become negativeand biosorption decreased. This observation also agreeswith the earlier reports on Cr(VI) removal by variousbiosorbents (Bai and Abraham 2001; Park et al. 2005b; Tewari et al. 2005). The acquisition of charge by the Table 2  Second order kinetic parameters for the sorption of Cr(VI) on  Aspergillus niger  Models  r  2 SSE SE ConstantsSobkowsk and Czerwinski 0.9307 19.8870 1.4861  k   =  0.00725  ±  0.00012 (min - 1 )Ritchie 0.9307 19.8870 1.4861  k   =  0.00725  ±  0.00012 (min - 1 )Blanchard et al. 0.9580 0.000026 0.0018  k   =  0.0001105  ±  0.000009(g mg - 1 min - 1 ) a  =  0.01888  ±  0.0026 (g mg - 1 )Ho and McKay 0.9580 0.000026 0.0018  q e  =  52.966  ±  0.9620 (mg g - 1 ) k   =  0.0001105  ±  0.000016 (g mg - 1 min - 1 )World J Microbiol Biotechnol (2009) 25:1413–1421 1417  1 3
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