Biosorption potential of driedPenicillium restrictum for Reactive Orange 122: isotherm, kinetic and thermodynamic studies

Biosorption potential of driedPenicillium restrictum for Reactive Orange 122: isotherm, kinetic and thermodynamic studies
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   Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol   83 :569–575 (2008) Biosorption potential of dried  Penicillium restrictum  for Reactive Orange 122:isotherm, kinetic and thermodynamic studies Semra Ilhan, 1 Cansu Filik Iscen, 2 Necmettin Caner 3 and Ismail Kiran 3 ∗ 1 Department of Biology, Faculty of Arts and Science, Eski¸ sehir Osmangazi University, 26480 Eski¸ sehir, Turkey  2 Department of Elementary Education, Faculty of Education, Eski¸ sehir Osmangazi University, 26480, Eski¸ sehir, Turkey  3 Department of Chemistry, Faculty of Arts and Science, Eski¸ sehir Osmangazi University, 26480 Eski¸ sehir, Turkey  Abstract BACKGROUND: This paper evaluates the biosorption of Reactive Orange 122 dye (RO 122) by dried  Penicilliumrestrictum  cells. The aim was to determine the pH, contact time, temperature and dye concentration for theapplicability of biomass as an alternative biosorbent for the removal of RO 122.RESULTS: Optimum initial pH and equilibrium time for RO 122 were determined as 1.0 and 75min at 25 ◦ C,respectively. The maximum biosorption capacity ( q  max ) of biomass obtained from the Langmuir fit was 180.7,190.1 and 219.8mgg − 1  biomass at 25, 40 and 50 ◦ C, respectively. Both Langmuir and Freundlich isotherm modelswere fitted to the experimental data at constant temperatures of 25, 40 and 50 ◦ C. The biosorption process wasfound to obey a pseudo-second-order kinetic model and was favourable at high temperatures.CONCLUSIONS: The biomass could be an alternative biosorbent to RO 122 dye removal because of havingadvantages of being easily cultivable, its low cost, high biosorption capacity with low biomass dosage (0.4g dm − 3 )and reasonably rapid biosorption rate. © 2008 Society of Chemical Industry Keywords:  Penicillium restrictum ; biosorption; Reactive Orange 122; isotherms; kinetics; thermodynamics INTRODUCTION Dyes are synthetic chemical compounds and havecomplex aromatic structures which contain differentgroups such as azo as chromophores combined withvarious reactive groups. 1 There are many structuralvarieties, such as acidic, basic, azo, diazo, disperse,metal complex and antraquinone-based dyes, 2 andthey are generally considered as a primary contributorto environmental pollution owing to their wide usein many areas. The major industries which utilizedye molecules to colour their final products aredye houses, textiles, cosmetics, food, rubber, leather,pharmaceutical, paper and printing industries. 3 Oncedyes are discharged into receiving waters, they notonly prevent photosynthetic activity in aquatic life byreducing light penetration 4 but also produce toxicamines by the reductive cleavage of azo linkages,causing severe effects on human beings throughdamaging the liver, kidneys, brain, reproductive andcentral nervous systems. 2 , 5 Therefore, their removalcauses a big environmental concern worldwide and issubjected to much scientific research.Traditional physical and chemical treatment pro-cesses used extensively to treat dyestuffs from textileand dye-containing effluents are adsorption by acti-vated carbon, flocculation, colour irradiation, coag-ulation, reverse osmosis, ultra filtration, sedimenta-tion, precipitation 6 and Fenton oxidation, 7 but theyare ineffective, especially for the removal of brightlycoloured, water-soluble reactive and acid dyes. 8 Thereason is that dyes show resistance to many chemicals,oxidizing agents and light. 9 The adsorption by acti-vated carbon is the most widely used process becauseofitshighadsorptioncapacity,surfaceareaandmicro-porous structure, 10 but its large-scale application ishampered by high operating costs,relatively high priceand problem with regeneration. 4 , 11 Over the past few decades, biosorption processesutilizing plant materials 10 and a wide variety of microorganisms in dead, pretreated and immobilizedforms as adsorbing agents 12 have attracted attentionas an effective low-cost alternative technology. This isbecause they are cheap to produce and carry a widerange of binding sites for toxic and harmful pollutantssuch as dye molecules. 13 They have been investigated ∗ Correspondenceto: Ismail Kiran,Department of Chemistry,Faculty ofArts and Science, Eski¸sehir Osmangazi University, Campus of Me¸selik, 26480Eski¸sehir, TurkeyE-mail:  Received 22 September 2007; revised version received 16 October 2007; accepted 16 October 2007   )Published online 5 February 2008 ;  DOI: 10.1002/jctb.1836 ©  2008 Society of Chemical Industry.  J Chem Technol Biotechnol   0268–2575/2008/$30.00  Semra Ilhan  et al  . for the removalof variousdyes from aqueoussolutionssuch as Basic Blue 4, 11 Astrazone Blue, 14 AcidRed 274, 15 Malachite Green, 16 Acid Red 57, 17 andReactive Black 5. 18 The term ‘biosorption’ refersto the removal of unwanted organic and inorganicspecies including metals, dyes and odour-causingsubstances by microbial biomass through passivetransport mechanisms which include complexation,physical adsorption and ion exchange. 19 Microbialcell surfaces carry various functional groups such asamino, phosphate, hydroxyl and carboxylate, whichare known to be responsible for the sequestration of hazardous materials from industrial effluents. 20 Inthisstudy,thebiosorptionofReactiveOrange122(RO 112) dye onto dried  Penicillium restrictum  biomasswas investigated in a batch system. The investigationcovered the determination of parameters which affectprocess efficiency to ascertain optimum values such asinitial pH and contact time. Two sorption isothermmodels,namelytheLangmuirandFreundlich models,were used to fit the equilibrium isotherm data.Biosorption kinetics and thermodynamics were alsoinvestigated and parameter values were derived. EXPERIMENTALPreparation of the biosorbent The filamentous fungus  P. restrictum  (wild type) wasisolated from an industrial wastewater treatment plantin Eski¸sehir, Turkey. The fungus was stored onagar–potato dextrose agar slants at 4 ◦ C. 21 A mediumfor growing  P. restrictum  was prepared by mixingsucrose (20g), Bacto peptone (5g), neopeptone (5g),KH 2 PO 4  (1g), NaNO 3  (1g) and MgSO 4 . 7H 2 O(0.5g) in distilled water (1dm 3 ). The pH of thegrowth medium was adjusted to 5.5 by the additionof 1mol L  − 1 HCl before autoclaving at 121 ◦ C forat least 20min. Erlenmeyer flasks containing theabove media (100cm 3 ) were inoculated with sporesuspension (1cm 3 ) obtained by shaking sterile water(10cm 3 ) with a mature slope of   P. restrictum  understerile conditions. Growth was allowed to proceedfor 7days at 25 ◦ C on a rotary shaker operating at120rpm. After the fungal growth, the biomass andculture medium were separated by filtration. Theresultingbiomasswaswashedseveraltimesthoroughlywith distilled water, spread on Petri dishes and driedin an oven at 60 ◦ C overnight. It was then powderedusing a mortar and pestle and sieved to select 150 µ mparticles for use as a biosorbent. Preparation of dye solution The dye used in this study was RO 122 (commercialname Sakofix Orange ME2RL) obtained fromBIRBOY textile company (Istanbul, Turkey) andused without further purification. The test solutionscontaining RO 122 dye were prepared by diluting1.0g dm − 3 of stock solution which was prepared bydissolving an accurate quantity of dye in bidistilledwater. Dye biosorption experiments Laboratory biosorption experiments were performedat biomass feed of 0.4g dm − 3 , different initial RO 122dye concentrations and various temperatures. Thebatch experiments were carried out in a stopperedconical flask (250cm 3 ) at an agitation speed of 200rpm on a magnetic stirrer. The biosorptioncapacity was determined by using the followingequation, taking into account the concentrationdifference of the solution at the beginning and atequilibrium: q e  = [ ( C  i − C  e ) ] xV m ( 1 ) where  C  i  and  C  e  are the initial and the equilibrium dyeconcentrations(mgdm − 3 ), V   isthevolumeofsolution(dm 3 ) and  m  is the amount of biosorbent used (g).First, the effect of solution pH on the biosorptioncapacity of RO 122 dye onto dried  P. restrictum biomass was examined by equilibrating the adsorptionmixture with dried biomass (0.02g) and 50cm 3 of 150mg dm − 3 RO 122 dye solution, adjusting the pHvalue between 1 and 10 for a prefixed time period.This was followed by assessment of the effect of equilibrium time varied between 10 to 120min onthe dye biosorption capacity of the biosorbent. Theoptimum pH and equilibrium time were determinedas 1.0 and 75min, respectively. The binding capacityof biomass was then assessed, varying the RO 122 dyeconcentration within the range 100–250mg dm − 3 and adjusting the pH to a value of 1.0, whichis the optimum pH. When the sorption procedurewas completed, the solutions were centrifuged at4500rpm for 10min and the supernatants were thenanalysed for residual RO 122 dye concentrationsusing a spectrophotometer (UV-visible, Cecil 4002,Cambridge, UK) at  λ max  488 nm. The solutionsconcerned were diluted to known concentrations toread the values before making the measurements.Finally, several experiments were conducted todeduce kinetic parameters as follows: a constantbiomass of 0.02g was weighed and mixed with 50cm 3 of 150mg dm − 3 RO 122 dye solutions at various timeintervals between 10 and 120min and temperatures of 25, 40 and 50 ◦ C. The concentration of RO 122 dyewas determined as described above. RESULTS AND DISCUSSIONEffect of pH pH is an important parameter for biosorption studiesand affects not only the biosorption capacity butalso the colour and solubility of dye solutions. Themaximum biosorption capacities of dried  P. restrictum biomass are plotted against the equilibrium pH inFig. 1using50mLof150mgdm − 3 initialdyesolutionand 0.02g biomass dose at 25 ◦ C for a prefixedtime period. As shown in this figure, the equilibriumbiosorption capacity of the biosorbent decreasedsharply from 101.73mgg − 1 biomass to 74.35mgg − 1 570  J Chem Technol Biotechnol   83 :569–575 (2008)DOI: 10.1002/jctb  RO 122 dye biosorption by  Penicillium restrictum biomass when the solution pH was changed from 1 to2 and this trend continued with increasing solutionpH from 2 to 6, causing the equilibrium uptakecapacity to drop from 74.35 to 15.55mgg − 1 biomass.The biosorption capacity further decreased beyondpH 6 and reached the lowest level of 4.13mgg − 1 biomass biosorption capacity at pH 10. From thisstudy the optimum pH is determined as 1, where themaximum biosorption capacity of dried  P. restrictum cells for RO 122 dye was determined as 101.73mgg − 1 biomass at 25 ◦ C. This effect is largely related to theanionic character of RO 122 dye. Weak base groupsin the biomass surface are protonated and acquirea net positive charge with diminishing solution pH.This causes a significantly high electrostatic attractionbetween the surface of dried  P. restrictum  cells and RO122 dye and, as a result, a high biosorption capacity.Lower biosorption capacity of RO 122 observedat basic pH is due to competition between excesshydroxyl ions and negatively charged dye ions for thebiosorption sites. 15 Effect of contact time Contact time is one of the important parametersfor successful deployment of the biosorbents for pH0 2 4 6 8 10 12   q    (  m  g  g    −    1    ) 020406080100120 Figure 1.  Effect of pH for the biosorption of RO 122 dye onto dried P. restrictum  cells at 25 ◦ C. t   (min)0 20 40 60 80 100 120 140   q    (  m  g  g    −    1    ) 020406080100120140160 25 ° C40 ° C50 ° C Figure 2.  Effect of equilibrium time for biosorption of RO 122 dyeonto dried  P. restrictum  cells at temperatures of 25, 40 and 50 ◦ C. practical application and rapid sorption is amongdesirable parameters. 22 Fig. 2 indicates the RO 122dye uptake by the biosorbent as a function of timeat pH 1.0 and different temperatures of 25, 40 and50 ◦ C. An uptake capacity of 59.47mgg − 1 biomasswas observed within 10min and then the sorptioncapacity was increased constantly with increasingtime. The equilibrium time was reached in 75min,when the biosorption capacity was 111.97mgg − 1 biomass at 25 ◦ C. Beyond the equilibrium time, thereis a steady decrease observed on the biosorptioncapacity. A similar trend was observed at 40 and50 ◦ C,whenthemaximumbiosorptioncapacitiesweredetermined as 118.81 and 133.82mgg − 1 biomass,respectively, in 75min. Therefore 75min is fixed asthe optimum contact time for studies carried out at25, 40 and 50 ◦ C. An increase in biosorption capacityobserved with increasing contact time is due toavailability of biosorption sites on the biomass surface,while a decrease in biomass capacity observed afterequilibrium time could be related to the desorptionof dye molecules from the biomass surfaces, probablycaused by repulsive forces between dye molecules atadjacent sites on the biomass surfaces. 15 Effect of initial dye concentration The initial concentration provides an importantdriving force to overcome resistances encounteredwhen all molecules are transferred between theaqueous and solid phases. 23 In this study, the RO 122dyeremovalcapacityofdried P. restrictum biomasswasinvestigated using RO 122 dye solutions ranged from100 to 250mg dm − 3 at a biosorbent concentrationof 0.4g dm − 3 , pH 1.0 and temperatures of 25,40 and 50 ◦ C. The equilibrium dye uptake capacityvalues (mg g − 1 biomass) are given in Fig. 3. Theequilibrium loading capacity increased from 97.28 to154.13mgg − 1 biomass asthe initial dye concentrationwas increased from 100 to 250mg dm − 3 , which is themaximum dye uptake value at 25 ◦ C. A similar trendwas observed at 40 and 50 ◦ C, reaching maximum C  o  (mg dm − 3 )0 50 100 150 200 250 300   q   e    (  m  g  g    −    1    ) 050100150200 25 ° C40 ° C50 ° C Figure 3.  The effect of initial RO 122 dye concentration forbiosorption of RO 122 dye onto dried  P. restrictum  cells at 25, 40 and50 ◦ C.  J Chem Technol Biotechnol   83 :569–575 (2008)  571 DOI: 10.1002/jctb  Semra Ilhan  et al  . loading capacities of 162.38 and 184.50mgg − 1 biomassat225mgdm − 3 initialdyeconcentration.Thebiosorption capacity decreased to a small extent to avalue of 158.56 at 40 ◦ C and 178.88mgg − 1 biomassat 50 ◦ C as the initial dye concentration was furtherincreased to 250mg dm − 3 . Therefore, the optimuminitial dye concentrations are determined as 250mgdm − 3 at 25 ◦ C and 225mg dm − 3 at 40 and 50 ◦ C. Theeffects could be explained as follows: at lower initialdye concentrations, all dye molecules could interactwith the binding sites on the biomass surface andhigh sorption rates occur, while at high initial dyeconcentrations binding sites on the biomass surfaceare saturated and no further biosorption occurs. Adecreaseobservedinthebiosorptioncapacityismainlydue to the repulsive forces between dye molecules atadjacent sites on the cell surface, resulting in removalof some dye molecules from the surface. 15 Effect of temperature Temperature has two main effects on the sorptionprocesses.Increasingtemperatureisknowntoincreasethe diffusion rate of the adsorbate molecules withinthe pores as a result of decreasing solution viscosityand will also modify the equilibrium capacity of theadsorbent for a particular adsorbate. 24 To investigatethe effect of temperature, the equilibrium biosorptioncapacity of RO 122 dye onto dried  P. restrictum  cellswas studied at three constant temperatures of 25, 40and 50 ◦ C (Fig. 2). An increase in temperature from25 to 40 and to 50 ◦ C leads to an increase in uptakecapacity of the biomass for dye molecules from 110.05to 118.81 and to 133.82mgg − 1 biomass, respectively,under optimum conditions of pH and contact time.This result indicated that the RO 122 dye biosorptionprocess onto dried  P. restrictum  cells was favoured athigher temperatures. Biosorption isotherms Two isotherm models – Langmuir and Freundlich – are used for the estimation of biosorption ratesbetween RO 122 dye and dried  P. restrictum  cells.The Langmuir isotherm model is a monolayeradsorption process developed for gas phase adsorptiononto the surface of glass and metals. It assumes thatthe adsorbent surface contains specific homogeneoussites which are energetically equivalent and distant toeach other. These sites can only hold one moleculeand no interactions between adsorbed moleculesat adjacent sites occur. The linearized Langmuirisotherm equation can be represented by the followingexpression: 25 1 q e = 1 q max +   1 q max  K  L    1 C  e ( 2 ) where  q max  is the maximum amount of adsorption(mg g − 1 ),  q e  (mg g − 1 ) and  C  e  (mg dm − 3 ) are theequilibrium RO 122 dye and solution concentrationsat equilibrium and  K  L   is the Langmuir adsorptionconstant (dm 3 mg − 1 ) related to the free energyof adsorption. The plot of 1 / q e  against 1 / C  e  of Eqn (2) should give a linear relationship from which  K  L   and  q max  can be determined from the slope1 / q max .  K  L   and the intercept 1 / q max , respectively.The Langmuir isotherm can also be expressed bymeans of a dimensionless constant,  R L  , a positivenumber referred to as the separation factor orequilibrium parameter, whose magnitude providesinformation about whether the biosorption processis spontaneous or non-spontaneous. The process isirreversible if   R L   is 0, favourable if   R L   is less than 1,linear if   R L   is 1 and unfavourable if   R L   is greater than1. It can be calculated by using Eqn (3). 26 R L   = 11 +  K  L  C  o ( 3 ) where  C  o  is the highest initial RO 122 dyeconcentration (mg dm − 3 ).The Freundlich isotherm model assumes thatadsorption takes place on heterogeneous surfaces andthe sorption capacity depends on the concentration of RO 122 dye at equilibrium. The linearized Freundlichisotherm equation 27 is shown asln q e  = ln  K  F + 1 n ln C  e  ( 4 ) where  K  F  and  n  are the Freundlich isotherm constants(dm 3 g − 1 ),whichcanbedeterminedfromtheinterceptand the slope, respectively, by plotting ln q e  againstln C  e  of Eqn (4). The constant  K  F  and slope 1 / n are defined as a sorption coefficient representingthe amount of dye molecules for a unit equilibriumconcentration and a measure of the sorption intensityor surface heterogeneity, respectively. A value of 1 / n = 1 shows that the partition between two phasesdoes not depend on the concentration, a value of 1 / n  <  1 corresponds to a normal L-type Langmuirisotherm, while 1 / n  >  1 indicates a cooperativesorption involving strong interactions between themolecules of adsorbate. 24 The values of   R L   are calculated using Eqn (3) as0.169at 25 ◦ C,0,118at40 ◦ Cand0.131at 50 ◦ C,andincorporatedinTable 1.Asthe R L   valuesliebetween0and 1, the biosorption process is said to be favourable.Plots of the linear form of Langmuir and Freundlichbiosorption isotherms of RO 122 dye obtained attemperatures of 25, 40 and 50 ◦ C are illustrated inFigs 4 and 5 and the isotherm model parameters are Table 1.  Isotherm constants for the biosorption of RO 122 dye ontodried  P. restrictum  cells at temperatures of 25, 40 and 50 ◦ C Langmuir Freundlich t   ( ◦ C)  q max  K  L  r  2L  R L  K  F  n r  2F 25 180.7 0.0197 0.94 0.169 22.7 2.799 0.9740 190.6 0.0300 0.92 0.118 40.7 3.723 0.9250 219.8 0.0265 0.93 0.131 37.0 3.192 0.94 572  J Chem Technol Biotechnol   83 :569–575 (2008)DOI: 10.1002/jctb  RO 122 dye biosorption by  Penicillium restrictum 1/  C  e 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020 0.022 0.024    1   /   q   e 0.0050.0060.0070.0080.0090.0100.01125 ° C40 ° C50 ° C Figure 4.  Langmuir plots for biosorption of RO 122 dye onto dried  P. restrictum  cells at temperatures of 25, 40 and 50 ◦ C. ln C  e 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4    l  n   q   e 25 ° C40 ° C50 ° C Figure 5.  Freundlich plots for biosorption of RO 122 dye onto dried P. restrictum  cells at temperatures of 25, 40 and 50 ◦ C. tabulated in Table 1. It is evident from these data thatboth Freundlich and Langmuir isotherm models havea good fit to the experimental data, with regressioncoefficients ( r  2 ) of 0.973, 0.936 at 25 ◦ C, 0.923, 0.919at40 ◦ Cand0.941,0.926at50 ◦ C,respectively.Thesemeanthatthesurfaceofdried P.restrictum cellscontainhomogeneous and heterogeneous biosorption patchesand that the biosorption process involves more thanone mechanism. Biosorption kinetic The kinetic studies have carried out to determine theefficiency of RO 122 dye biosorption onto  P. restrictum cells. Various kinetic models including the pseudo-first-order, pseudo-second-order and intraparticlediffusion 28 were tested for the experimental data toelucidate the biosorption mechanism. Among them,the pseudo-second-order kinetic model 29 was found t   (min)0 20 40 60 80    t   /  q    (  m   i  n  m  g  g    −    1    ) 25 ° C40 ° C50 ° C Figure 6.  Pseudo-second-order kinetic plots for biosorption of RO122 dye onto dried  P. restrictum  cells at temperatures of 25, 40 and50 ◦ C. to be applicable and can be written as follows: t q t  = 1 k q 22 + 1 q 2 t   ( 5 ) where  q 2  is the maximum biosorption capacity (mgg − 1 ) for the pseudo-second-order sorption,  q t   is theamount of RO 122 dye biosorbed at time  t   (mgg − 1 ),  k 2  is the equilibrium rate constant of pseudo-second-order sorption (mg g − 1 min − 1 ). An adequatepseudo-second-order kinetic model should show alinearplotof  t  / q t   against t   withareasonablemagnitudeof the regression coefficient  r  2 . Values of   q 2  and  k 2  canbe easily deduced from the slope and intercept of theplot of   t  / q t   versus t   (Fig. 6), respectively.Thepseudo-second-orderkineticparametersforthebiosorption of RO 122 dye onto dried  P. restrictum cells are presented in Table 2. The magnitude of the regression coefficient  r  2 changed between 0.974and 0.995 at constant temperatures of 25, 40  J Chem Technol Biotechnol   83 :569–575 (2008)  573 DOI: 10.1002/jctb
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