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Biosorption of Drimarine Blue HF-RL using raw,pretreated, and immobilized peanut hullsSaima Noreena, Haq Nawaz Bhattia, Sana Nausheena, Muhammad Zahida & Sadia Asima

a Environmental Chemistry Laboratory, Department of Chemistry and Biochemistry,University of Agriculture, Faisalabad 38040, Pakistan, Tel. +92 41 9200161/3319, Fax: +9241 9200764Published online: 01 Aug 2013.

To cite this article: Saima Noreen, Haq Nawaz Bhatti, Sana Nausheen, Muhammad Zahid & Sadia Asim (2014) Biosorption ofDrimarine Blue HF-RL using raw, pretreated, and immobilized peanut hulls, Desalination and Water Treatment, 52:37-39,7339-7353, DOI: 10.1080/19443994.2013.823118

To link to this article: http://dx.doi.org/10.1080/19443994.2013.823118

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Biosorption of Drimarine Blue HF-RL using raw, pretreated, andimmobilized peanut hulls

Saima Noreen, Haq Nawaz Bhatti*, Sana Nausheen, Muhammad Zahid, Sadia Asim

Environmental Chemistry Laboratory, Department of Chemistry and Biochemistry, University of Agriculture,Faisalabad 38040, PakistanTel. +92 41 9200161/3319; Fax: +92 41 9200764; email: haq_nawaz@uaf.edu.pk

Received 6 March 2013; Accepted 3 July 2013

ABSTRACT

The aim of this study is to establish an economical and environment friendly method for theremoval of reactive dye from wastewater. This study was carried out for the removal of Dri-marine Blue HF-RL using raw, nitric acid treated, and immobilized peanut hulls in bothbatch and column modes. In batch study, different process parameters like pH, biosorbentdose, initial dye concentration, contact time, and temperature were optimized. The pH (2),biosorbent dose (0.05 g), initial dye concentration (400, 200, 200mg/L), contact time (90, 120,120min), and temperature (30˚C) were optimized for raw, nitric acid treated, and immobi-lized peanut hulls. The biosorption data have been analyzed using Langmuir, Freundlich,Temkin, Doubinin–Radushkevich, and Harkins–Jura isotherms. The isothermal data followedthe Langmuir model. The biosorption processes conformed to the pseudo-second-order ratekinetics. Different thermodynamic parameters were estimated during thermodynamic study.The results showed the exothermic and spontaneous nature of biosorption process. Thecolumn study was also investigated for making the process more applicable on industrialscale. The optimum bed height (4.5 cm), flow rate (1.8mL/min), and initial dye concentration(100mg/L) were found in column study. Thomas and Bed depth service time models werefitted well to the experimental data in continuous process. The FTIR spectrum confirmed thepresence of –NH2 and –C=O groups in the biomass structure responsible for interactionbetween biomass and dye molecules. The results proved that the peanut hulls in differentforms behave as efficient and cost-effective biosorbent for the removal of reactive dyes.

Keywords: Biosorption; Peanut hulls; Pretreatments; Kinetics; Equilibrium isotherms;Thermodynamics

1. Introduction

The visible, toxic, and stable nature of differentsynthetic dyes has given motivation to search for newmethods of treatment to avoid their discharge toenvironment [1]. The discharge of dyestuff into the

environment causes a disturbance in the ecosystem. Itcan produce various esthetic problems as well asreduction in the sunlight penetration into water byreflecting it, thereby reducing the self-purificationpotential of water bodies [2]. As a result, few biologi-cal degradation mechanisms in water bodies can bedestroyed to produce ecological balance [3]. Dyeing

*Corresponding author.

1944-3994/1944-3986 � 2013 Balaban Desalination Publications. All rights reserved.

Desalination and Water Treatmentwww.deswater.com

doi: 10.1080/19443994.2013.823118

52 (2014) 7339–7353

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industries generate extremely colored contaminatedwastes. Textile industries mostly utilized the syntheticdyes for dyeing processes and these dyes are alsoused as additives in different petroleum products [4].Approximately, ten thousand different dyes and pig-ments are utilized industrially and more than 0.7mil-lion tones of these dyes are formed annually in world.It is expected that about 10–15% of these syntheticdyes are discharged in the wastewater through thedyeing processes. Most of them are lethal for waterbody life [5]. These can cause harmful effects on theliving systems due to their toxic, carcinogenic, andallergenic nature [6]. Several reactive dyes are utilizedin different industries like textile, leather, rubber,paper, etc. Among different types of dyes, the brightcolored and highly water-soluble reactive dyes createlot of problems [7,8].

Mostly, reactive dyes are utilized in textile indus-tries due to their easy dyeing methods and formationof covalent bonds with fibers, especially cellulose.Mostly, these dyes are lethal to biotic populations inwater ecosystem [9–11]. These dyes have complicatedaromatic structure due to which these show more sta-bility against biodegradation [12]. The techniques uti-lized for elimination of dyes from wastewater include,oxidation, chemical degradation, coagulation, biologi-cal treatments, adsorption, etc. These techniques fallunder wide categorization of physical and chemicaltechniques [13]. However, biosorption is most effectivetechnique for elimination of dyes from wastewater.All conventional techniques including physical andchemical require high cost while biosorption is verycost-effective technique and also eco-friendly [14]. Anumber of economic biosorbents have been utilizedfor the removal of dyes from waste water viz., ricehusk, cotton waste, canola hull, oil palm fruit, citrusbiomass, etc. [15,16]. A peanut hull is an agriculturalwaste which is found abundantly and could beexploited for the treatment of wastewater. Peanuthulls contain lipid, mineral, cellulose, and polyphenolslike catechol, m-trihydroxybenzene, etc. which containdifferent functional groups like carboxyl and phenolichydroxyl groups through which bind the dyes fromwastewater [17]. Sometimes the biosorbents in nativeform do not give better results due to less availabilityof functional moieties on them [18].

Different physical and chemical treatments aregiven to the biosorbents for improving their biosorp-tion [19]. These modifications may improve ordecrease their biosorption capacities but mostly thesetreatments increase the surface area of biosorbent thatenhanced their biosorption capacity [20]. Biosorbentsare heated, boiled, autoclaved, etc. in physical treat-ment while treated with acids, alkalis, salts,

surfactants, and organic compounds in chemicaltreatment [13]. Biosorbent may be used in immobi-lized form for improving biosorption capacity. Severalpolymeric substances are utilized for immobilizing thebiosorbents like polyacrylamide, alginate, carboxymethyl cellulose, polysulfone, etc. [21–23].

The present work investigates the possibility of pea-nut hulls as biosorbent for the removal of DrimarineBlue HF-RL from aqueous solution. The effect of vari-ous process parameters like medium pH, temperature,initial dye concentration, biosorbent dose, and contacttime on the biosorption capacity of raw, pretreated, andimmobilized peanut hulls was investigated. Differentequilibrium and kinetic models were also applied toreach mechanistic approach of biosorption process.

2. Materials and methods

2.1. Pretreatment and immobilization of biosorbent

The biosorbent was modified using different physi-cal and chemical treatments for improvement in itsbiosorption capacity for reactive dye. Peanut hullswere boiled and heated for 30min during physicaltreatments, while it was shaked with 5% solution ofacids, alkalis, surfactants, organic solvents, and differ-ent chelating agents for 1 h at 120 rpm and 30˚C inchemical treatments. The biosorbent was treated withHCl, CH3COOH, H2SO4, and HNO3 in acid treatmentand KOH, NaOH, NH4OH, were used for modifyingscreened biosorbent in alkalis treatment. Differenttypes of surfactants, anionic SDS, cationic CTAB, andnonionic Triton-X 100 were utilized for modification.Various chelating agents like Polyethylenimine (PEI),glutaraldehyde, EDTA, and organic solvents likeCH3OH and C6H6 were used in chemical treatment.After shaking, all these modified biosorbents were col-lected by filtration and then washed 2–3 times withdistilled water. After washing, all these were dried inoven at 60˚C for 24 h and then saved for further utili-zation. Immobilization of peanut husk was done withsodium alginate (2%) solution [24,25].

2.2. Preparation of stock solution of dye

The reactive dye Drimarine Blue HF-RL was giftedfrom commercial market of Faisalabad city, Pakistan.For stock solution preparation, firstly weighed the 1 gof dye keenly on analytical balance and then dissolvedin few mL of distilled water in 1,000mL measuringflask and then made the volume up to 1,000mL. Afterpreparation, the stock solution was saved in airtightglass bottle for further use. Different dilutions thatrequired were made from that stock solution easily.

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2.3. Batch sorption study

The batch biosorption study was carried out foroptimizing different process parameters like pH (2–9),biosorbent dose (0.05–0.30 g), initial dye concentration(10–600mg/L), contact time (0–180min), and tempera-ture (30–60˚C) for the biosorption of Drimarine BlueHF-RL using different forms of peanut (raw, HNO3

treated, and immobilized). Each batch biosorptionexperiment was run in 250-mL Erlenmeyer flasks con-taining 50mL of dye concentration solution and bio-sorbent dose at constant pH and temperature byshaking in orbital shaker at 120 rpm. After shaking,the supernatant was collected by centrifugation andthen analyzed the dye anions concentration by usingUV–visible spectrophotometer (Shimadzu Brand UV-4000) at kmax = 608 nm. Each experiment wasperformed in duplicate and the average results wereused for making calculations. The biosorption capacitywas estimated by using the following equation:

qe ¼ ðC0 � CeÞ VW

ð1Þ

where qe is the biosorption capacity (mg/g) of biosor-bent for dye while the C0 and Ce is the initial andequilibrium concentrations of dye (mg/L), respec-tively. V is the dye solution volume (L) and W (g) isthe biosorbent dry weight [4].

2.4. Biosorption equilibrium studies

Modeling was carried out on the biosorption equi-librium data for investigating the mechanism ofbiosorption process. Different equilibrium modelslike Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, and Harkins–Jura were applied.

2.5. Biosorption kinetics studies

The biosorption kinetics of Drimarine Blue HF-RLwere studied using different forms of peanut (raw,HNO3 treated, and immobilized). Different modelslike pseudo-first-order, pseudo-second-order, andintraparticle diffusion were applied on the kineticdata.

2.6. Thermodynamics studies

Thermodynamic studies were carried out to inves-tigate the spontaneity and feasibility of biosorptionprocess and different thermodynamic parameters likeenthalpy change, Gibbs free energy change, andentropy change were determined.

2.7. Column study

The continuous biosorption experiments wereperformed using the Pyrex glass columns of 43 cmheight with 1.2 and 2.2 cm internal diameter. The setup for conducting experiments were made of threecolumns that were parallel to each other. Thesecolumns were fed by multichannel peristaltic pumpat maintained constant flow rate in the range of1.8–36mL/min and at constant temperature 30˚C. Atthe end of column, glass wool was put to create littlesupport. All the fittings and tubes that interconnectedto each other were made of Polytetrafluoroethylene[26]. The column was packed by certain amount ofbiosorbent to get the required bed height in the2.5–4.5 cm range. The pH of dye solution was adjustedby utilizing 0.1M HCl and NaOH. The certain concen-tration dye solution in the 50–100mg/L range at con-stant pH 2 and at certain flow rate of 1.8–5.4mL/minwas pumped through column in each experiment. Thesamples were collected after regular time intervals inthe test tubes and then the dye anions concentrationwas analyzed by using the double-beam UV–visiblespectrophotometer (Shimadzu Brand UV-4000) atkmax = 608 nm [27]. The different experiments were car-ried out to optimize the process parameters like bedheight, initial dye concentration, and flow rate.

3. Results and discussion

The biosorption capacity of peanut hulls forDrimarine Blue HF-RL was determined in batch andcolumn studies. In batch mode different models likeequilibrium, thermodynamic, and kinetic were appliedand breakthrough curves were estimated in columnmode.

3.1. Effect of modifications/treatments

Various physical and chemical modifications weregiven to peanut hulls to improve its biosorption capac-ity for Drimarine Blue HF-RL. These physical andchemical modifications of peanut hulls either increasedor decreased its biosorption capacity in comparisonwith the biosorption capacity of raw peanut hulls. Thefollowing increasing order showed the effect of differ-ent treatments on peanut hulls: CTAB<SDS<KOH<NaOH<EDTA<NH4OH< glutaraldehyde <methanol <Triton X-100 < raw<heating<benzene <boiling <CH3COOH<HCl <H2SO4<HNO3. The bio-sorption capacity of peanut hulls decreased by treat-ment with alkali. The decrease might be due to theelectrostatic repulsion among the negative charges ofdye and peanut hulls surface negative charge, resultingfrom deprotonation of functional groups [13]. Modifica-

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tion with acids increased the biosorption capacity ofpeanut hulls in comparison with its native form. Itmight be due to the electrostatic attraction among theanions of dye and positive charges on the surface ofpeanut hulls, produced by protonation of functionalgroups [22]. The nitric acid treated peanut hulls showedmaximum biosorption capacity for Drimarine Blue HF-RL. Methanol modification reduced the biosorptioncapacity of peanut hulls, due to ester formation [24].Glutaraldehyde treatment decreased the biosorptioncapacity of peanut hulls due to the formation of cross-linkage between the surface functional groups [25]. Sur-factant modification also reduced the biosorptioncapacity of peanut hulls. The nonionic surfactant TritonX-100 did not produce any significant effect on biosorp-tion capacity as compared to untreated peanut hulls.But cationic surfactant CTAB and anionic surfactantSDS modifications caused significant reduction in bio-sorption capacity of peanut hulls. It might be due tocreation of hindrance by surfactants in attachment ofdye anions on the peanut hull surface [4]. EDTA treat-ment also caused reduction in biosorption capacity ofpeanut hull because it might be chelated the surfacefunctional groups of peanut hull and reduced theiraccess for dye molecules. Organic solvent treatmenteither enhances the biosorption capacity or producenegligible effect on it. Benzene enhanced the biosorp-tion capacity by removing the lipids and protein con-tents that covered the surface, so after their removal,large number of active sites were created whichenhanced the biosorption capacity [14]. Boiling andheating of peanut hulls showed improved biosorptioncapacity than untreated peanut hulls. It might be due tothe removal of different minerals and organic com-pounds that masked the binding sites. PEI is good che-lating agent. The PEI contains higher number of aminegroups that enhance its chelating ability. So biosorptioncapacity of peanut hulls increased by treating with PEI[20]. It might be due to the electrostatic attractionamong the amine groups and dye molecules. The cross-linking between the chelating agent and biosorbentenhanced the ease of access of amine groups for dyeanions [28].

3.2. Effect of pH

The pH is a major factor that affects the biosorp-tion capacity of biosorbent during the treatment ofwastewater [29]. Biosorption process depends on thepH because it affects the functional groups that pres-ent on the surface of biosorbents and also influencethe mechanism of biosorption. For studying pH effecton the biosorption capacity of peanut hulls forDrimarine Blue HF-RL, experiments were conducted

with different pH (2–9) range and the results areshown in Fig. 1. The raw, nitric acid treated, andimmobilized peanut hulls showed maximum biosorp-tion capacity of 14.26, 17.59, and 25mg/g), respec-tively, at lower pH (2.0). By increasing pH thebiosorption capacity of all forms of biosorbentsdecreased. The decrease in biosorption capacityincrease in pH might be due to the destruction oflarge number of cationic sites on biomass surface thatresulted in less electrostatic attractions between dyeanions and biomass and hence less dye removal [13].An acidic pH was observed during the removal ofAcid Orange 7 and Remazol Black 5 reactive dyesusing novel biosorbent [10]. A similar trend of pHwas also observed during the elimination of reactiveazo dyes by untreated, treated, and immobilizedCitrus sinensis waste as biosorbent [4].

3.3. Effect of biosorbent dose

The biosorbent dose plays an important role in thedetermination of biosorption capacity of the biosorbentfor the given initial dye concentration [11]. The effectof biosorbent dose (0.05–0.30 g) was studied on thebiosorption of Drimarine Blue HF-RL using differentforms of peanut hull (raw, nitric acid treated, andimmobilized) at pH 2, 50mg/L initial dye concentra-tion, and 30˚C temperature. It was found that the allforms of peanut hulls showed the maximumbiosorption capacity with 0.05 g biosorbent dose(Fig. 2). The biosorption capacity values decreasedfrom 36.4 to 8.3mg/g for raw, 40 to 13mg/g for nitricacid treated, and from 19.06 to 6.47mg/g forimmobilized peanut hulls by increasing the biosorbentdose. The reason might be the reduction in the surfacearea and increment in path length of diffusion due toaggregation of bioosrbent particles, which resulted inthe decrease in biosorption capacity [4]. A similar trend

q e (m

g/g)

0

5

10

15

20

25

30

2 3 4 5 6 7 8 9pH

Raw nitric acid treat immobilized

Fig. 1. Effect of pH on biosorption of Drimarine BlueHF-RL using raw, nitric acid treated, and immobilizedpeanut hulls.

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of dose was observed during the biosorption of textiledyes using iron based sludge [30]. A low dose of bio-sorbent was also found for the removal of textile dye(Reactive Red 195) by using Pinus sylvestris L [31].

3.4. Effect of initial dye concentration

The initial dye concentration acts as an importantparameter for the investigation of biosorption capacityin biosorption process. It shows the relation betweennumber of binding sites that present on the surface ofbiosorbent and the dye anions [32]. The effect of initialdye concentration (10–600mg/L) on the biosorptioncapacity of different forms of peanut hull (raw, nitricacid treated, immobilized) for Drimarine Blue HF-RLwas investigated at pH 2 and at constant temperatureusing optimized biosorbent dose (0.05 g). The resultsshowed that the biosorption capacity of all peanuthulls forms increased by increasing the initial dyeconcentration and then remained constant. Further, nosignificant effect on biosorption capacity was foundby increasing initial dye concentration. The raw, nitricacid treated, and immobilized peanut hullsshowed maximum biosorption capacity of 50, 55, and38mg/g, respectively, at 400, 200, and 200mg/L(Fig. 3). The increase in biosorption capacity withincreasing initial dye concentration might be due theexistence of more vacant active sites on the biosorbentsurface at low value of initial dye concentration andthe number of these sites was reduced by increasingconcentration. When all sites were occupied and thenthe biosorption capacity remained constant andfurther increase produced no effect on biosorptioncapacity [11]. A similar trend was observed duringthe biosorption of malachite green using chitinhydrogels [33].

3.5. Equilibrium biosorption isotherms

Isotherms are the equilibrium relations betweenthe concentration of the adsorbate on solid phase andits concentration in the liquid phase. The equilibriumbiosorption data of Drimarine Blue HF-RL usingdifferent forms of peanut hull (raw, nitric acid treated,and immobilized) have been analyzed usingLangmuir, Freundlich, Dubinin–Radushkevich (D–R),Temkin, and Harkins–Jura isotherms.

3.5.1. Langmuir biosorption isotherm

The Langmuir biosorption isotherm explains thebiosorption of dye molecules on the surface of the bio-sorbent by forming the monolayer without showinginteractions with the nearby dye molecule molecules.The linear form of Langmuir biosorption isotherm isgiven as follows:

Ce

qe¼ 1

qmbþ Ce

qmð2Þ

The model was applied on the biosorption processof Drimarine Blue HF-RL using different forms ofpeanut hulls (raw, nitric acid treated, and immobi-lized) as biosorbent. The regression line was obtainedby plotting the Ce/qe vs. Ce and the values of differ-ent parameters like qm and b were determined usingthe value of slope and intercept obtained from theplot [30].

3.5.2. Freundlich biosorption isotherm

The Freundlich biosorption isotherm explains thebiosorption of dye molecules on the heterogeneous

q e (m

g/g)

0

10

20

30

40

50

60

70

10 25 50 75 100 150 200 400 600Concentration (mg/L)

Raw nirtic acid treat Immobilized

Fig. 3. Effect of initial dye concentration on biosorption ofDrimarine Blue HF-RL using raw, nitric acid treated, andimmobilized peanut hulls.

q e (m

g/g)

Raw nirtic acid treat Immobilized

05

1015202530354045

0.05 0.1 0.15 0.2 0.3Biosorbent dose (g)

Fig. 2. Effect of biosorbent dose on biosorption ofDrimarine Blue HF-RL using raw, nitric acid treated, andimmobilized peanut hulls.

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surfaces of biosorbent. The following equationrepresents the linear form of Freundlich biosorptionisotherm:

log qe ¼ logKf þ 1

nlogCe ð3Þ

This biosorption isotherm was applied on the bio-sorption process of Drimarine Blue HF-RL using dif-ferent forms of peanut hulls. The straight line wasproduced by plotting the log qe against log Ce and thevalues of different constants like n and KF were deter-mined using the slope and intercept values obtainedfrom plot [34].

3.5.3. Temkin biosorption isotherm

Temkin isotherm describes the effects of few indi-rect interactions between the dye molecules on thebiosorption isotherm. This model suggests an equaldistribution of binding energies over the number ofthe exchanging sites on the surface. The linear form ofTemkin biosorption isotherm is shown in followingexpression:

qe ¼ B lnAþ B lnCe ð4Þ

where qe represents the biosorption capacity (mg/g),Ce represents the concentration of Drimarine Blue HF-RL at equilibrium (mg/L), and A and B are Temkinconstants while the constant B represents the biosorp-tion heat value [11]. That model was also applied forthe interpretation of equilibrium biosorption data ofDrimarine Blue HF-RL.

3.5.4. D–R biosorption isotherm

D–R biosorption isotherm describes that the sur-face of biosorbent is not homogeneous. This model isutilized for the calculation of porosity apparent freeenergy. The following equation represents the linearform of the D–R biosorption isotherm:

ln qe ¼ ln qm � be2 ð5Þ

where qm represents the theoretical saturation capacityand e is the Polanyi potential that is estimated byusing the following equation [35].

e ¼ RT ln 1þ 1

Ce

� �ð6Þ

The D–R biosorption isotherm was also applied onthe equilibrium biosorption data and its fitness waschecked.

3.5.5. Harkins–Jura biosorption isotherm

Harkins–Jura isotherm explain the heterogeneity ofpores present on the surface of biosorbent due to thatreason the formation of multiple layers take place.The linear form of this isotherm is represented asfollows.

1

qe2¼ B

A

� �� 1

A

� �logCe ð7Þ

The fitness of those biosorption isotherms waschecked to know the biosorption mechanism ofDrimarine Blue HF-RL. The results of variousisotherm parameters are shown in Table 1. Theequilibrium results for the biosorption of DrimarineBlue HF-RL showed Langmuir model fitted well forraw, nitric acid treated, and immobilized peanut hullswith the high values of R2 (0.89, 0.99, and 0.99). TheRL values also showed that the process of biosorptionwas favorable. The data showed that the Frendlich,Temkin, and Harkins–Jura models were poor fitted onthe equilibrium data by possessing low values of R2

and more difference between the theoretical maximumbiosorption values and experimental values. D–Rmodel was fitted on the immobilized and pretreatedpeanut with high value of R2 (0.90, 0.93) andpossessed close value of theoretical maximumbiosorption capacity to experimental qmax value.

3.6. Effect of contact time

The equilibrium time plays an important role in thedesigning of economical systems for the treatment ofwastewater [7]. The effect of contact time(0–180min) on the biosorption capacity of raw, nitricacid treated, and immobilized peanut hulls wasdetermined at pH 2, 50mg/L initial dye concentration,and at 30˚C temperature. The raw, nitric acid treated,and immobilized peanut hulls showed maximumbiosorption capacity (36, 37, and 26.99mg/g) after 90,120, and 120min. The results are shown in Fig. 4. Theresults indicated that the biosorption capacityincreased very rapidly at the start of biosorptionprocess then became slow and finally reached atequilibrium. This is due to the availability of largenumber of vacant active sites at the start of biosorptionprocess and then these sites reduced after some timeand at equilibrium all sites were covered [4]. A similareffect of contact time has been observed in thebiosorption of methylene blue using peanut husk inbatch study [36].

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3.7. Kinetic studies

The kinetic results obtained during the biosorptionof Drimarine Blue HF-RL using different forms ofpeanut hulls (raw, nitric acid treated, and immobi-lized) were analyzed by intraparticle diffusion [37],pseudo-first-order [38], and pseudo-second-order [39]models. The fitness of these models was checked byexamining the value of correlation coefficient R2.

3.7.1. Pseudo-first-order kinetic model

The basis of this model is that it shows the directrelation between the concentration of dye and time.The change in concentration of dye with respect totime is proportional to the power one.

The linear form of pseudo-first-order kinetic modelis given as follows:

logðqe � qtÞ ¼ log qe � K1t=2:303 ð8Þ

where qe is the biosorption capacity at the equilibriumwhile qt is the biosorption capacity at time t. k1 is thepseudo-first-order rate constant and its unit is 1/min.

3.7.2. Pseudo-second-order kinetic model

Pseudo-second-order explains the mechanism ofreaction for complete range of equilibrium timeresults. It depends upon the capacity of biosorption ofmaterial used as biosorbent. The linear form of thepseudo-second-order kinetic model is given asfollows:

t=qt ¼ 1=K2q2e þ t=qe ð9Þ

where qe is the biosorption capacity at the equilibriumwhile qt is the biosorption capacity at time t. The k2(g/mgmin) is second-order rate constant ofbiosorption process.

3.7.3. Intraparticle diffusion model

Intraparticle diffusion model explains the all stepsrequire for reaching the adsorbate molecules from theaqueous solution to the surface of biosorbent. Firstly,molecules come to the surface of biosorbent, attach onthe outer surface and then diffuse into the pores ofthe biosorbent surface. At last molecules attach to thebinding active sites of the biosorbent. The process ofbiosorption can take place in single step or in multiplesteps. The equation of intraparticle diffusion kineticmodel can be expressed as:

05

1015202530354045

0 5 10 15 30 45 60 90 120 180

q e (m

g/g)

Time (min)

nitric acid treated raw immobilized

Fig. 4. Effect of contact time on biosorption of DrimarineBlue HF-RL using raw, nitric acid treated, andimmobilized peanut hulls.

Table 1Equilibrium parameters for the biosorption of DrimarineBlue HF-RL onto raw, nitric acid treated, and immobilizedpeanut hulls

Isotherm models Drimarine Blue HF-RL

Raw Nitricacidtreated

Immobilized

Freundlich

KF 2.04 2.98 2.81

n 2.34 3.44 4.18

R2 0.42 0.71 0.77

Langmuir

qm (The) (mg/g) 55.86 53 38.61

qm (exp)(mg/g) 49.99 55 38

Ka (l/mg) 0.02 0.136 0.14

RL 0.103 0.035 0.03

R2 0.8908 0.99 0.99

Dubinin–Radushkevich

Qm (mg/g) 47.00 47.84 33.91

K (mol2kJ�2) �0.018 �0.001 �0.0014

E (kJmol�1) 5.22 16.66 19.23

R2 0.57 0.90 0.93

Temkin

A (l/g) 1.393 4.06 6.87

B 291.77 308.48 488.45

R2 0.69 0.84 0.89

Harkins–Jura

A �18.24 �243.90 �232.55

B �2.25 �2.17 �2.32

R2 0.20 0.450 0.51

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qt ¼ Kpit1=2 þ Ci ð10Þ

Here, Ci represents the thickness of boundary layerand the Kpi (mg/g) is the rate constant of intraparticlediffusion. All above three kinetic models were appliedto get information about the rate of biosorption pro-cess of Drimarine Blue HF-RL using different forms ofpeanut hulls (raw, nitric acid treated, and immobi-lized). The fitness of kinetic model was checked bycomparing the coefficient of determination (R2) valuesand the calculated biosorption capacity value (qcal)with the experimental value (qexp). The resultsobtained are shown in Table 2. The results showedthat the pseudo-second-order showed the best fitnessdue to high value of R2 (0.99, 0.99, and 0.97) for raw,nitric acid treated, and immobilized peanut hulls Thepseudo-first-order kinetic model showed poor fitnessfor raw and immobilized peanut hulls but showedgood fit for nitric acid treated peanut hulls. Theintraparticle diffusion model also showed the poor fit-ness. By kinetic study, it was suggested that thepseudo-second-order was the best fit model.

3.8. Effect of temperature

Temperature acts as an indicator to know about thenature of biosorption process whether the process isendothermic or exothermic [32]. The effect of tempera-ture (30–60˚C) on the biosorption of Drimarine Blue

HF-RL using different forms of peanut hull (raw, nitricacid treated, and immobilized) was investigated atoptimum pH 2, biosorbent dose 0.05 g, and 50mg/Linitial concentration of Drimarine Blue HF-RL. Theresults are shown in Fig. 5. The results showed that thebiosorption capacity decreased from 36.4 to 25mg/gfor raw, 36.96 to 33mg/g for nitric acid treated, and17.5 to 15mg/g for immobilized peanut hulls byincreasing the temperature from 30 to 60˚C. The reduc-tion in biosorption capacity with increasing tempera-ture showed that the biosorption process wasexothermic. In the process of biosorption, weak interac-tion forces (van der Waals forces and hydrogen bond-ing) are involved and increase in temperature resultsin breakdown of adsorptive forces which result indecrease in dye removal at higher temperatures [34]. Asimilar trend of temperature was observed during thebiosorption of acid blue 40 by using cone biomass ofThuja orientalis [40].

3.9. Thermodynamic parameters

The different thermodynamic parameters show thedependence of biosorption process on the temperature.The feasibility of biosorption process was determinedusing various thermodynamic parameters like Gibbsfree energy change (DG0), enthalpy change (DH0), andentropy change (DS0). The Gibbs free change DG0 wasestimated using the following equation:

DG0 ¼ �RT lnKd ð11Þ

where Kd represents the equilibrium biosorptionconstant and T represents the value of absolutetemperature. The following expression represents therelation among different thermodynamic parameters:

Table 2Kinetic parameters for the biosorption of Drimarine BlueHF-RL onto raw, nitric acid treated, and immobilizedpeanut hulls

Kinetic models Raw HNO3

treatedImmobilized

Pseudo-first-order

k1(l/min) �0.022 �0.03 �0.02

qe exp (mg/g) 37 36 26.99

qe cal (mg/g) 9.170 38.46 19.69

R2 0.603 0.93 0.94

Pseudo-second-order

k2(g/mgmin) 0.008 0.002 0.001

qe cal (mg/g) 37.59 38.61 30.21

qe exp (mg/g) 37 36 26.99

R2 0.99 0.9927 0.97

Intraparticle diffusion

kpi (mg/gmin1/2) 1.28 2.60 2.15

Ci 23.41 7.59 3.16

R2 0.84 0.89 0.88

05

1015202530354045

30 35 40 45 50 60

q e(mg/

g)

Temperature (0C)

Raw nitric acid treated Immobilized

Fig. 5. Effect of temperature on biosorption of DrimarineBlue HF-RL using raw, nitric acid treated, andimmobilized peanut hulls.

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lnKd ¼ DS0=R� DH0=R� 1=T ð12Þ

The value of thermodynamic parameter DH0 andDS0 was calculated by plotting the ln Kd vs. 1/T [29].The values of different thermodynamic parameters forthe biosorption of Drimarine Blue HF-RL using differ-ent forms of peanut hull (raw, nitric acid treated, andimmobilized) at different temperatures are listed inTable 3. The negative value of DG0 represented thespontaneous nature of biosorption process ofDrimarine Blue HF-RL with raw, nitric acid treated,and immobilized peanut hulls. These values showedthat the process was thermodynamically favorable.The minus value of DH0 (�24.84, �10.3, and �7.07)kJ/mole indicated that the biosorption of DrimarineBlue HF-RL on the raw, nitric acid treated, and immo-bilized peanut hulls was exothermic in nature whilethe negative value of DS0 (�0.075, �0.026, �0.028)indicated the reduction in randomness occurred asbiosorption proceeded [41].

3.10. Effect of salt and heavy metal ions

The effect of different concentrations of NaCl waschecked on the biosorption capacity of peanut hullsfor the biosorption of Drimarine Blue HF-RL at pH 2,50mg/L initial concentration of at constant tempera-ture (30˚C). The results showed that the biosorptioncapacity decreased from 36.4 to 28.91mg/g byincreasing the salt concentration from 0.2 to 1%. Thereason might be the reduction of electrostaticattractive forces among the dye anions and thebinding functional groups due to increased number ofions [4]. Similar effect of salt was also found for theremoval of reactive blue 49 using capsicum annumseeds [42]. The industrial wastewater also contains the

heavy metal ions which affect the biosorption of reac-tive dyes. The effect of heavy metal ion (Pb2+) on thebiosorption capacity of peanut hulls was investigatedusing different concentrations of Pb(NO3)2 (0.2–1%)under preoptimized conditions. The results showedthat the biosorption capacity of peanut hullsdecreased from 36.4 to 26.5mg/g with increasing Pb2+

concentration (0.2–1%). The results are shown inFig. 6. The decrease in biosorption capacity might dueto the competition between the Pb2+ and the mole-cules of dye for the same binding sites of the bioosr-bent [43].

3.11. Desorption study

The desorption study increases the efficiency ofbiosorption process and makes it more economicaland eco-friendly by regeneration of the biosorbent[44]. The results obtained from batch study showedthat the maximum biosorption was obtained at pH 2or in the acidic range. So it was assessed that desorp-tion would occur at higher pH value. Sodium hydrox-ide (NaOH) solution of different concentrations (0.2–1M) was used without adjusting its pH at 30˚C and120 rpm. The results of biosorption desorption experi-ments showed that the 70% desorption of DrimarineBlue HF-RL occurred with 0.2M NaOH solution. Thechoice of eleunt used for desorption is very important.

3.12. Fixed-bed column study of Drimarine Blue HF-RL

The optimization of three process parameters likebed height, flow rate, and initial dye concentration forthe biosorption of Drimarine Blue HF-RL using rawpeanut hulls was carried out in Pyrex glass columnhaving 2.2 cm diameter and 43 cm length. The break-

Table 3Thermodynamic parameters for the biosorption of Drimarine Blue HF-RL onto raw, nitric acid treated, and immobilizedpeanut hulls

Drimarine Blue HF-RL

Temp (K) Raw HNO3 Immobilized

�DGo �DHo �DSo �DGo �DHo �DSo �DGo �DHo �DSo

303 2.48 24.84 0.075 2.62 10.3 0.026 1.55 7.07 0.028

308 1.48 2.16 1.69

313 0.572 2.08 1.96

318 0.211 1.75 2.18

323 0.107 1.76 2.27

333 0.221 1.83 2.34

⁄DGo (kJ/mole); ⁄⁄DHo(kJ/mole); ⁄DSo (kJ/molK).

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through biosorption capacity Q50% was calculated byusing the following formula:

The breakthrough biosorption capacity (Q50%) ofDrimarine Blue HF-RL for 4.5 cm bed height, 50mg/Linitial dye concentration, and 1.8mL/min flow ratewas found to be 6.75mg/g. The all biosorptioncapacity values are listed in Table 4.

3.12.1. Effect of bed height

The optimization of bed height (2.5–4.5 cm) for thebiosorption of Drimarine Blue HF-RL using raw pea-

nut hulls at constant pH 2, 50mg/L initial dye concen-tration, 1.8mL/min flow rate, and at constanttemperature was done (Fig. 7). The results indicatedthat three breakthrough curves were obtained for threebed heights (2.5, 3.5, and 4.5 cm). These were obtainedby plotting the ratios of Cout (final) and Cin (initial) or(Cout/Cin) with time (min). The results showed that thebiosorption capacity increased by increasing the bedheight from 2.5 to 4.5 cm. Maximum biosorptioncapacity was obtained at 4.5 cm. This bed height wasconsidered as optimum bed height and used in subse-quent experiments for the optimization of other pro-cess parameters. The biosorption capacity valuesobtained at 2.5, 3.5, and 4.5 cm bed heights were 3.60,4.84, and 6.75mg/g, respectively. It was observed thatthe breakthrough time was also enhanced withincreasing bed height because the increased quantityof biosorbent attributed more number of bindingactive sites which expanded the zone of mass transfer

[45]. The breakthrough time (80, 140, and 240) min wasrequired for getting maximum biosorption ofDrimarine Blue HF-RL using 2.5, 3.5, and 4.5 cm bedheight. The reason might be the increased surface areafor biosorption by increasing quantity of biosorbent inhigher bed height in column which enhanced the bio-sorption capacity. The less bed height caused the axialdispersion instead of transfer of mass. Due to this dyemolecules had not got the suitable time for diffusioninto whole biosorbent so dye diffusion was decreased[46]. The results for optimization of bed height areindicated in Table 4.

3.12.2. Effect of flow rate

Flow rate is the major parameter in the selection ofbiosorbent for application in continuous treatmentprocess of wastewater on large scale. The effect ofdifferent flow rates (1.8, 3.6, and 5.4mL/min) wasstudied for the removal of Drimarine Blue HF-RLusing the peanut hulls in column at pH 2 and 4.5 cmbed height. The experiments were performed at the30˚C temperature. The breaks through curves wereproduced by plotting the Cout/Cin ratios of DrimarineBlue HF-RL vs. time (t) min (Fig. 8). The dataobtained from these curves is shown in Table 4. Theresults represented the decrease in biosorptioncapacity from 6.75 to 5.06mg/g by increasing the flow

Break through capacityðQ50%Þ ¼ Time for break through ðat 50%Þ�flow rate� initial conc. of dye solution

Mass of biosorbent in the bedð13Þ

Fig. 7. Effect of bed height on biosorption of DrimarineBlue HF-RL by peanut hulls.

0

5

10

15

20

25

30

35

40

No metal 0.20% 0.40% 0.60% 0.80% 1%

q e (m

g/g)

Metal concentration %

Fig. 6. Effect of heavy metal ions (Pb2+) on biosorption ofDrimarine Blue HF-RL using raw peanut hulls.

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rate from 1.8 to 5.4mL/min and also reduced thebreakthrough time from 240 to 60min. The is due theincrement in biosorption zone speed at higher flowrate which produced the reduction in time that isessential for reaching the required concentration atbreakthrough point [47,48]. The reduction in biosorp-tion capacity might be due to the reduction in equilib-rium time for biosorption due to high value of flowrates [49]. Similar trend was observed for flow rate inthe removal of methylene blue by using the Posidoniaoceanica (L.) dead leaves [50].

3.12.3. Effect of concentration

The effect of different initial Drimarine BlueHF-RL concentrations (50, 75, and 100mg/L) on thebiosorption capacity of peanut hulls in column wasstudied at pH 2, 1.8mL/min flow rate, and constanttemperature 30˚C. The breaks through curves wereobtained by plotting the time t (min) vs. Cout/Cin

ratios. The results obtained from these breakthrough

curves are shown in Table 4. The results showed thatthe biosorption capacity increased from 6.75 to7.87mg/g by increasing the initial concentration ofDrimarine Blue HF-RL from 50 to 100mg/L (Fig. 9).The information about breakthrough time was alsoobtained from the breakthrough curves. The break-through time decreased from 240 to 140min byenhancing the initial concentration of Drimarine BlueHF-RL from 50 to 100mg/L. The increase in initialconcentration of dye, increased the rate of dye loadingand caused reduction in biosorption zone length [51].Similar trend was observed for the biosorption ofmethylene blue by using jackfruit leaf powder [52].

3.13. Kinetic modeling of experimental data

3.13.1. Bed-depth service time model

The BDST model is the simple model and tellsabout the linearity among the bed height (Z) and theservice time (t). It is represented by the followingequation:

Table 4Column adsorption capacities (Q50%) of Drimarine Blue HF-RL at different experimental conditions of flow rate (mL/min), bed height (cm), and initial dye concentration (mg/L)

Inlet conc. (mg/L) Break point (50%) (min) Flow rate (mL/min) Bed height (cm) Adsorption capacity (mg/g)

50 80 1.8 2.5 3.60

50 140 1.8 3.5 4.84

50 240 1.8 4.5 6.75

50 100 3.6 4.5 5.62

50 60 5.4 4.5 5.06

75 180 1.8 4.5 7.59

100 140 1.8 4.5 7.87

Fig. 9. Effect of concentration on biosorption of DrimarineBlue HF-RL by peanut hulls.

Fig. 8. Effect of flow rate on biosorption of Drimarine BlueHF-RL by peanut hulls.

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t ¼ N0Z=C0U � 1=KaC0 lnC0

Cb

� 1

� �ð14Þ

In the above equation, Cb represents the DrimarineBlue HF-RL solution concentration (mg/L) at 50%breakthrough point and Ci represents the initial con-centration (mg/L) of Drimarine blue HF-RL solution.V (cm/min) represents the linear velocity, N0 (mg/L)represents the biosorption capacity while the Ka

(L/mgmin) represents the rate constant. In the BDSTmodel, t-Z at 0.2, 0.4, and 0.6 values of Cb/Cin wasplotted by maintaining 1.8mL/min flow rate, 50mg/Linitial concentration of Drimarine Blue HF-RL at con-stant temperature. The values of all constants areshown in Table 5. The plot gave the straight linethrough which the high values of coefficient of deter-mination (R2 = 0.99, 0.98, and 0.99) were obtained for0.2, 0.4, and 0.6 Cb/Cin, respectively. It showed the

high validity of BDST model on the biosorption ofDrimarine Blue HF-RL by using the peanut hull incolumn. From the plot, the values of different con-stants were calculated with the help of intercept andslope. The values of slope and intercept for respectiveCb/Cin ratio are listed in Table 5. The biosorptioncapacity values N0 (mg/L) were calculated with thehelp of slope and the value of rate constant Ka

(L/mgmin) from intercept by keeping the V and Ci asconstant. The value of rate constant Ka gives the infor-mation about transfer rate of Drimarine Blue HF-RLfrom solution to the peanut hull surface [53]. Theresults indicate that the biosorption capacity value(N0) was increased from 114.64� 10�3 to 229.2� 10�3

by increasing the Cb/Cin from 0.2 to 0.60 at 1.8mL/min flow rate and 50mg/L of Drimarine Blue HF-RLsolution concentration while the rate constant wasdecreased from 4.62� 10�4 to 0.81� 10�4 [54].

Fig. 10. FTIR spectra of native and Drimarine Blue HF-RL loaded peanut hulls.

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3.13.2. Thomas model

Thomas model is the most common model whichis utilized for the description of column breakthroughdata [55]. The linear form of that model is given asfollows:

lnðC0=Ct � 1Þ ¼ KTh � q0XW=Q� KTh � C0 � t ð15Þ

The Thomas model was applied on the break-through data that obtained at the different bed heightsof peanut hull, flow rates, and initial Drimarine BlueHF-RL concentrations. In that model, ln(C0/Ct� 1)plotted vs. t and gave the straight line. By usingstraight line, the values of correlation coefficient (R2)and different parameters (qo, Kth) were calculated. Thefitness of model was checked from the value of (R2)and also by comparing the theoretical biosorptioncapacity value with the experimental value. Table 6represents the summarized form of all parametersobtained by the Thomas model for the biosorption ofDrimarine Blue HF-RL using peanut hulls at differentbed heights, flow rates, and initial concentrations ofdye solution. The results showed that the biosorptioncapacity values q0 increased from 2.13 to 5.19mg/gby increasing the bed height from 2.5 to 4.5 cm andalso increased from 5.19 to 9.73mg/g by increasingthe initial Drimarine Blue HF-RL concentration from50mg/L to 100mg/L but the value of kinetic coeffi-cient (kth) was decreased from 4.16 to 3.03 (L/mgmin)

in first case and from 3.03 to 1.02 (L/mgmin) insecond case. The contrast was observed in the case offlow rate, here the kth value increased from 3.03 to3.38 (L/mgmin) and q0 value decreased from 5.19 to4.80 by increasing the flow rate from 1.8 to 5.4mL/min [56]. Similar behavior was also observed for thebiosorption of phenol by using the immobilized acti-vated sludge [57]. So the Thomas model shows betterapplicability for that biosorption process where theoutside and inside diffusions will not the rate deter-mining step. The higher value of R2 and the compari-son of calculated biosorption capacity with theexperimental biosorption capacity showed that theThomas model was fitted on the data obtained fromdifferent bed heights, flow rates, and initial dyeconcentrations in column.

3.14. FTIR study

FTIR analysis is used for the identification ofsurface functional groups and all possible interactionsamong the functional groups on the biosorbent surfaceand the dye molecules in the biosorption process. TheFTIR spectrum of native peanut hull and DrimarineBlue HF-RL loaded peanut hull was studied in the400–4,000 cm�1. The obtained peaks are shown inFig. 10(a) and (b). The broad peak obtained in nativepeanut hull spectrum appearing at 3348.92 cm�1

is due to the presence of –OH stretching on the

Table 6Parameters of Thomas model at different experimental conditions for Drimarine Blue HF-RL

Bed height (cm) Flow rate (mL/min) Initial dye conc. (mg/L) Qexp (mg/g) Qcal (mg/g) KTh (L/mgmin) R2

2.5 1.8 50 3.60 2.13 4.166 0.989

3.5 1.8 50 4.84 4.79 2.89 0.980

4.5 1.8 50 6.75 5.19 3.03 0.987

4.5 3.6 50 5.62 5.08 3.44 0.982

4.5 5.4 50 5.06 4.80 3.38 0.993

4.5 1.8 75 7.59 9.07 1.29 0.979

4.5 1.8 100 7.87 9.73 1.02 0.987

Table 5The calculated BDST model constants for the adsorption of Drimarine Blue HF-RL on peanut hulls (V= 1.8mL/min andCo = 50mg/L)

Cb/Ci a (min/cm) b (min) N0� 10�3 (mg/L) Ka� 10�4 (L/mg min) R2

0.20 40 60 114.64 4.62 0.99

0.40 50 68.33 143.3 1.18 0.98

0.60 80 100 229.2 0.81 0.99

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biosorbent surface. The disappearance of this peak indye loaded spectrum indicated the presence of �OHstretching on the peanut hull surface that interactedwith the dye molecules during the biosorption pro-cess. The appearance of peak in native peanut hullspectrum in the range of 1640.01–1512.33 cm�1 indi-cated the presence of N=N stretching on peanut hullsurface and its appearance at 1630.64 cm�1 with lessintensity in dye loaded spectrum indicated its interac-tion with the dye molecules. The peak observed innative peanut at 1026.06 cm�1 may be produced dueto the presence of C�O group in the alcohol and car-boxylic acids on the peanut hull surface. This peakinteracted with dye molecules, so new peak appearedat 1031.90 cm�1 with less intensity in dye loaded spec-trum. The peaks that appeared below 1,000 cm�1 can-not be identified easily because it is the finger printregion and showed complicated vibrating interactionsystems [30]. The peaks showed that the peanut hullmajorly contained the polysaccharides, lipids, andproteins having various functional groups like car-boxyl, hydroxyl, and amino. The biosorption of Dri-marine Blue HF-RL took place by the possibleinteractions with these functional groups.

4. Conclusion

In present study, the biosorption of Drimarine BlueHF-RL was carried out using the different forms ofpeanut hull (raw, nitric acid treated, and immobilized).It was found that the peanut hulls could be used as anefficient and economical biosorbent for the removal ofDrimarine Blue HF-RL from aqueous solution. Thesebiosorbent showed good biosorption capacity at theoptimum pH, biosorbent dose, contact time,temperature, and initial dye concentration. The fitnessof Langmuir biosorption isotherm showed the mono-layer formation of dye on the biosorbent surface. Thepseudo-second-order kinetic model fitted well on thebiosorption data. The thermodynamic study indicatedthat the biosorption process was exothermic andspontaneous in nature. The presence of salt reducedthe biosorption while the presence of metal ionsincreased the biosorption. The effect of bed height,flow rate, and initial dye concentration was alsoinvestigated in column study. BDST and Thomasmodel also showed the good fitness on the columnexperimental data. Seventy percent desorption wasobtained by using 0.2M NaOH solution. FTIR studyindicated the presence of different functional groupson the peanut surface and all possible interactionsamong the dye anions and binding active sites onbiosorbent surface.

Acknowledgments

The authors are thankful to Higher EducationCommission (HEC) of Pakistan for financial assistanceunder project no. 20-159/R7D/09/1841 and IndigenousPhD Fellowship Program.

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