This article was downloaded by: [City College Library]On: 03 March 2014, At: 08:40Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Environmental TechnologyPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/tent20

Treatment influence on green coconut shells forremoval of metal ions: pilot-scale fixed-bed columnGiselle S. C. Raulinoa, Carla B. Vidala, Ari Clecius A. Limaa, Diego Q. Melob, Juliene T.Oliveirab & Ronaldo F. Nascimentob

a Department of Hydraulic and Environmental Engineering, Federal University of Ceará, Ruado Contorno, S/N Campus do Pici, Bl. 713 – CEP: 60451-970, Fortaleza, CE, Brazilb Department of Analytical Chemistry and Physical-Chemistry, Federal University of Ceará,Rua do Contorno, S/N Campus do Pici, Bl. 940 – CEP: 60451-970, Fortaleza, CE, BrazilPublished online: 27 Feb 2014.

To cite this article: Giselle S. C. Raulino, Carla B. Vidal, Ari Clecius A. Lima, Diego Q. Melo, Juliene T. Oliveira & RonaldoF. Nascimento (2014): Treatment influence on green coconut shells for removal of metal ions: pilot-scale fixed-bed column,Environmental Technology, DOI: 10.1080/09593330.2014.880747

To link to this article: http://dx.doi.org/10.1080/09593330.2014.880747

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Environmental Technology, 2014http://dx.doi.org/10.1080/09593330.2014.880747

Treatment influence on green coconut shells for removal of metal ions: pilot-scalefixed-bed column

Giselle S. C. Raulinoa, Carla B. Vidala, Ari Clecius A. Limaa, Diego Q. Melob, Juliene T. Oliveirab

and Ronaldo F. Nascimentob∗

aDepartment of Hydraulic and Environmental Engineering, Federal University of Ceará, Rua do Contorno, S/N Campus do Pici,Bl. 713 – CEP: 60451-970, Fortaleza, CE, Brazil; bDepartment of Analytical Chemistry and Physical-Chemistry, Federal University of

Ceará, Rua do Contorno, S/N Campus do Pici, Bl. 940 – CEP: 60451-970, Fortaleza, CE, Brazil

(Received 2 July 2013; accepted 3 January 2014 )

This work investigates copper, nickel and zinc ion biosorption in single- and multi-component systems in a fixed-bed columnusing green coconut shells (CS). Approximately 85% of biosorbents are in a particle size ranging from 0.25 to 2 mm.Operational parameters selected include a flow rate of 200 mL min−1 and a bed height of 100 cm, which were selected for ashorter execution time and good adsorption capacity. Empty-bed contact time and Thomas models were applied, showing agood fit with the experimental data. The column adsorption capacity increased after the green CS powder was treated in acolumn with NaOH at a concentration of 0.1 mol L−1. The highest values of adsorption capacities founded were 0.69, 0.45and 0.39 mmol L−1 for Cu(II), Ni(II) and Zn(II), respectively, using green CS treated inside a column with NaOH of 0.1 M.The pH and chemical oxygen demand were monitored in the treatment solution and indicated that the adjustment of theseparameters is necessary before disposal of these solutions. A study of desorption using an acid solution was carried out forrecovery of metal ions.

Keywords: biosorption; green coconut shells; metal ions; wastewater; biosorbent treatment

1. IntroductionHeavy metal ions are known to be toxic and carcinogenic toliving organisms. They are not degradable and can accumu-late in the environment where they manifest their toxicity.Because of its mobility, metal ions are very difficult to tracewhen they are introduced into the ecosystem, and the ulti-mate destination of these metal ion species is frequentlyunknown.[1–3]

Among the processes for removing toxic metals fromaqueous effluents are chemical precipitation, flocculation,carbon adsorption, ion exchange, reverse osmosis andelectrodialysis.[3–7] These methods present disadvantages,including high cost or production of sludge with a high metalconcentration which is difficult to dispose of.[8,9]

Adsorption using low-cost materials is emerging asan economically attractive potential treatment for toxicmetal removal and recovery.[2,8] Lignocellulosic mate-rials are examples of low-cost materials with excellentmechanical properties that may originate from agriculturalor industrial waste.[2,9] Due to the high organic mat-ter content and the large volume of these agricultural orindustrial wastes, the improper disposal of these materi-als can contaminate water bodies and soil.[8,10] Many of

∗Corresponding author. Email: ronaldo@ufc.br

these agricultural or industrial waste materials have beeninvestigated for potential use as a biosorbent, includingcarrot waste, peanut shells, rice, nuts and crushed sugarcane, among others.[2,8,11–14]

One problem with the use of lignocellulose-containingmaterials for wastewater treatment is the high tannin con-tent. These compounds add colour to water, an unde-sirable characteristic in the effluent.[8,10] Some studiesof metal ion removal with lignocellulosic materials pro-posed treatments of these lignocellulosic materials toincrease their adsorption capacity.[6,9,15–18] However, thequality of the final solutions resulting from these treat-ments is not monitored, and the solutions are not treatedfurther.

The aim of this work was to investigate the treat-ment influence on green coconut shells (CS) using afixed-bed system for the removal of metal copper, nickeland zinc ions in aqueous solution. The adsorption capac-ity of the treated biosorbent was determined in single-and multi-component solutions and equilibrium modellingof Thomas and empty-bed contact time (EBCT) wasapplied. The treatment solutions were monitored for pHand COD.

© 2014 Taylor & Francis

Dow

nloa

ded

by [

City

Col

lege

Lib

rary

] at

08:

41 0

3 M

arch

201

4

2 G.S.C. Raulino et al.

2. Materials and methods2.1. BiosorbentThe green CS (Cocos nucifera) was supplied by EmbrapaTropical-CE (EMBRAPA/CE – Brazil) in its powderedform with particle sizes less than 5 mm. To study the dis-tribution of biosorbent particle sizes, a mass of 90.0017 gof biosorbent was weighed and placed at the top of asieving tower composed of sieves for various particlesizes (5-2/2-0.84/0.84-0.25/0.25-0.15/0.15-0.106/0.106-0.075/0.075-0.062/0.062-0.045/below 0.045 mm), over-lapping in a descending manner. The tower was then stirredfor 15 min. The fractions retained in the different sieveswere weighed carefully.[19]

2.2. Chemicals and solutionsFor the adsorption study, the synthetic solutions of Cu(II),Ni(II) and Zn(II) (Carlo Erba, Italy) were prepared from thefollowing salts: Cu(NO3)2 · 3H2O, Zn(NO3)2 · 6H2O andNi(NO3)2 · 6H2O, analytical grade (VETEC, São Paulo,Brazil). The reagents sodium hydroxide (Merck, São Paulo,Brazil) and nitric acid (VETEC, São Paulo, Brazil) wereused.

Single- and multi-component solutions of metal ions(copper, zinc and nickel) were prepared in concentra-tions of approximately 200 mg L−1 of Cu(II), Ni(II) andZn(II) from their respective salts in water (from WaterSupply Company). The water was untreated to pre-pare a synthetic sample as similar to a real effluentas possible. A large volume of solution was used ineach experiment (approximately 70 L). The character-istics of the water used in this work were measuredand are described as follows: pH = 7.12; conductivity =631 μS cm−1; calcium = 16.8 mg L−1; magnesium =21.87 mg L−1; chloride = 137.55 mg L−1; hardness = 132mg L−1 and total dissolved solids: 305 ppm.

Solutions of NaOH (0.1 mol L−1) and HNO3(0.1 mol L−1) were used in the treatment of the biosorbent,and a solution of HNO3 (0.5 mol L−1) was used as an eluentfor metal ions adsorbed on the material.

2.3. Adsorption columnThe adsorption studies were performed in a fixed-bedsystem after treatment with different solutions (NaOH(0.1 mol L−1), HNO3 (0.1 mol L−1) or water). A peristalticpump (model Watson-Marlow Sci-Q 323) was used to con-trol the flow rate on the poly(vinyl chloride) (PVC) column(100 and 160 cm × 62 cm ID) filled with the biosorbent. Thesolution was pumped through the column in an upward flow.All experiments occurred at room temperature (27 ± 2◦C).

The apparent density (ρap) of the bed was determined byAmerican Society for Testing and Materials Method D2854,and the apparent volume (Vap) for a given mass was cal-culated. The packing density (ρE) (the ratio between thetotal mass of particles (ML) and the volume of the empty

column (VL) was used to calculate the porosity (ε) of thebed, according to Equation (1)):

ε = 1 − ρE

ρap= VL − Vap

VL, (1)

where ρE is the packing density, ρap is the apparent density,VL is the total volume (internal) of the empty column and Vapis the total volume of the bed particles (apparent volume).

The maximum adsorption capacity of the biosorbent isgiven by Equation (2) [19]:

Q = [(C0/MM) × Fm]ms

∫ t=x

t=0

(1 − C

C0

)dt, (2)

where Q is the maximum adsorption capacity (mmol g−1),C0 is the initial concentration of the solution, MM is themolar mass, C is the concentration of adsorbate at a cer-tain volume, ms is the mass of biosorbent (g), Fm is thevolumetric flow (L min−1) and t is the time (min).

2.4. Effect of flow rate and bed heightThe biosorbent used was washed with water and dried atroom temperature before its use in the column. The weightused is referred to the dry mass.

Flow rates of 100, 200 and 300 mL min−1 with a bedheight of 100 cm were studied. The column was filledwith 480 g of biosorbent, and a multi-component syntheticsolution was percolated through it.

Two bed heights were studied: 100 and 160 cm, filledwith 480 and 600 g of biosorbent, respectively. Multi-component synthetic solution was percolated through thecolumn at a flow rate of 200 mL min−1.

Aliquots of 50 mL of column effluent solution werecollected every 10 min, and the residual concentrations ofmetal ions were analysed by atomic absorption spectropho-tometry (AAS).

2.5. Treatment influence on biosorbentTwo procedures were carried out: treatment of biosorbentoutside the column and treatment of biosorbent inside thecolumn.

2.5.1. Treatment outside the columnIn the first study, the coconut shells were used untreated(CS).

A second study was conducted with the CS washed withwater out of the column (CSWO). A mass of raw CS wasplaced in a container with water at a ratio of 1:3. This mix-ture was stirred for 1 h, filtered and then the biosorbentmaterial was dried at room temperature.

In the third study, the CS was washed with NaOH(0.1 mol L−1) out of the column (CSBO). A mass of biosor-bent was placed in a container with a solution of NaOH(0.1 mol L−1) at a ratio of 1:3. This mixture was stirred for

Dow

nloa

ded

by [

City

Col

lege

Lib

rary

] at

08:

41 0

3 M

arch

201

4

Environmental Technology 3

1 h, filtered, washed with water to remove the excess basicsolution, filtered again and the material was then dried atroom temperature.

For the above-mentioned three studies, a multi-component synthetic solution was percolated throughthe column under the following conditions: flow rateof 200 mL min−1, initial concentration of metal ions200 mg L−1, 480 g of untreated or treated CS. Aliquotsof 50 mL were collected every 10 min for obtaining thebreakthrough curves. The concentrations of metal ions weredetermined for each aliquot collected.

2.5.2. Treatment in the columnThe column was filled with CS and washed: with watercoconut shell washed with water inside the column (CSWI)and with NaOH (0.1 mol L−1) coconut shell washed withbasic solution inside the column (CSBI).

In the first study, 20 L of water was percolated throughthe column filled with 402 g of CS (CSWI). Fractionswere collected every 10 min, and the pH and COD weredetermined to measure the residual organic matter.

In the second study, 11 L of NaOH solution(0.1 mol L−1) was percolated through the column, filledwith 402 g of CS powder (CSBI), at a flow of 150 mL min−1.Then, water (20 L) was percolated through the column toremove the excess of basic species. Fractions were collectedevery 5 min, and the pH and COD were measured.

For the above-mentioned two studies, a multi-component synthetic solution at a concentration of200 mg L−1 was percolated through the column (100 cm bedheight) after treatments. Aliquots of 50 mL were collectedevery 10 min, and the pH and concentration of metal ionswere determined.

The per cent mass loss was calculated and was found tobe 6% for treatment with water and 17% for treatment withNaOH. The adsorption capacities of materials treated insidethe column were calculated considering the cited values ofmass loss.

2.6. Breakthrough curves for single componentBreakthrough curves for single-component solutions ofmetal ions (copper, nickel and zinc) were evaluated. First,the biosorbent was subjected to CSBI treatment. Then,the single-component synthetic solution of copper, nickeland zinc was percolated through the column. Aliquots of50 mL were collected every 10 min and single-metal ionconcentrations were determined.

2.7. Column regenerationAfter CSBI treatment and column saturation with multi-element synthetic solution, the metal ion desorption was

carried out with HNO3 solution (0.5 mol L−1). The concen-tration of metal ions was analysed by an AAS, model GBC933 plus, in an air-acetylene flame.

2.8. Fixed-bed column modellingIn this study, Thomas and EBCT models were used topredict the performance of the column.

2.8.1. Empty-bed contact timeIn some systems on a real scale where default behaviouris not observed, the breakthrough curve depends on thecolumn length. This dependence can be determined by per-forming experiments on a pilot-scale column at the sameflow rate, varying the lengths of the biosorbent bed. Thebreakthrough times are then determined from the ruptureconcentration. The EBCT is a measure of how much timea parcel of fluid spends in the column, on the basis that thecolumn contains no solid packing.[19,20] The EBCT is rep-resented by Equation (3). Another important parameter isthe biosorbent usage rate (BUR), that is, the ratio betweenthe weight of biosorbent in the column and the amount ofliquid passed into the column at the time of breakthrough(Equation (4)).[19]

EBCT (min) = VL

H× Asec, (3)

where VL is the total volume of the empty column (mL), His the hydraulic loading and Asec is the bed cross-sectionalarea.

Biosorbent usage rate = ML

Vb, (4)

where ML is the total mass of biosorbent inside the col-umn (g) and Vb is the volume of treated solution at thebreakthrough point (L).

2.8.2. Thomas modelThis model assumes a behaviour of continuous flowand uses the Langmuir isotherm for equilibrium and thereversible second-order kinetics reaction. The Langmuirisotherm is applicable for favourable and unfavourableadsorption conditions. Traditionally, the Thomas model isused to determine the maximum adsorption capacity ofbiosorbent in continuous systems. The Thomas model isexpressed by Equation (5).[20–23]

CC0

=[

11 + exp

] [kt(q0mc − C0Ve)

Fm

]. (5)

The adsorption capacity of the bed (q0) and the coefficient(Kt) may be obtained from the intercept and slope, respec-tively, of a curve obtained by plotting ln(C/C0 − 1) as afunction of t or Ve from the breakthrough point (Cb) until the

Dow

nloa

ded

by [

City

Col

lege

Lib

rary

] at

08:

41 0

3 M

arch

201

4

4 G.S.C. Raulino et al.

exhaustion point (Cx). The linearized form of the Thomasmodel is given by Equation (6):

ln[(C0/C) − 1] = Ktq0ms

Fm− KtC0t, (6)

where C is the adsorbate concentration at a determinatevolume (mg L−1); C0 is the initial solution concentration(mg L−1); Kt is the Thomas rate constant (mL mg−1 min−1);q0 is the maximum solid phase concentration (mg g−1), i.e.the maximum adsorption capacity; ms is the amount ofbiosorbent (g); Fm is the volumetric flow rate (L min−1);and Ve is the effluent volume (L).

3. Results and discussion3.1. Characterization of the biosorbent bedThe contact surface between the biosorbent and the liquidphase as well as the biosorbent particle size plays an impor-tant role in the phenomenon of adsorption.[4,24] GreenCS powder was submitted to a particle size determination.Approximately 85% of the biosorbent was in a particle sizeranging from 0.25 to 2 mm. Rosa et al.,[25] performing thesame type of analysis, found a value of 78% at the sameparticle size range. Sousa et al.,[18] studying the removalof metal ions Cu(II), Ni(II), Zn(II), Pb(II) and Cd(II) bygreen CS powder, found no significant effect on removalefficiency for metals studied in the particle size rangingfrom 0.15 to 0.25 mm.

The results of determination of some physical prop-erties of the biosorbent bed are described below for thebed heights of 100 and 160 cm, respectively: apparent den-sity, 0.188 g cm−3 for both; packing density, 0.159 and0.124 g cm−3; particle volume of 2553 and 3191 cm3; andporosity of the bed of 0.154 and 0.338.

3.2. Effect of flow rate and bed heightThe experimental and theoretical breakthrough curvesobtained for flow rates (100, 200 and 300 mL L−1) areshown in Figure 1.[26] The breakthrough and exhaustionvolume (chosen, respectively, as 5% and 90% of initial con-centration for all three metal ions) observed are larger forcopper than for zinc and nickel, due to higher affinity ofCu(II) by biosorbent surface, and a larger time period isrequired to reach the exhaustion volume, in contrast forNi(II) and Zn(II). Gao et al. [27] found a similar behaviourin Cu(II), Ni(II), Cd(II) and Zn(II) removal by oxidizedcarbon nanotubes. According to them, the removal pro-cess is related to such factors as the surface chemistry ofthe adsorbent, the initial concentration of ions, the com-ponents in the adsorption system and the ratio of the metalion species in solution and the redox reactions on the carbonsurface involving metals might affect negatively the amountadsorbed.[27]

The results shown in Table 1 revealed that with increasein flow rate (100–300 mL min−1), the adsorption capacitydecreased for Cu, Ni and Zn ions. Higher adsorption capac-ity values of 0.23 mmol g−1 for Cu(II), 0.07 mmol g−1 forNi(II) and 0.07 mmol g−1 for Zn(II) were obtained for a flowrate of 100 ml min−1. On the other hand, when flow velocityincreased three times, the percentage removal decreases at26.0%, 28.5% and 29.5%, respectively, for each metal ion.

A similar trend was observed by Shahbazi et al. [28] inPb(II), Cu(II) and Cd(II) removal by functionalized meso-porous silica. According to them, this is because metalions leave the column before the equilibrium stage can beachieved by reducing the performance of the column. Incontrast, Revathi et al. [3] observed that by increasing theflow rate, the adsorption capacity and Thomas constant wereincreased using the Ceralite IR 120 ion exchange resin forthe removal of Ni(II),Cu(II) and Zn(II) ions from syntheticelectroplating rinse water solutions.

It is known that the increase in the flow rate implies areduction in the hydraulic retention time (HRT) of metalions inside the column. According to Cooney,[19] HRT isa typical parameter of design and operation of bed fixedcolumns, and the usual residence times on column rangefrom 15 to 30 min. Larger residence times can lead to adecrease in the solute removal, while shorter times do notallow an effective contact interaction to occur between thesorbent and sorbate.[5,19] It is important that HRT be higherthan equilibrium time that is determined in batch experi-ments, allowing a time of contact large enough between theadsorbent and adsorbate. In this study, the HRT decreasedfrom 30 to 10 min when the flow rate increased from 100 to300 mL min−1.

According to results obtained by the breakthroughcurves, the flow rate of 200 mL min−1 was chosen forthe following studies because it provided high adsorptioncapacity and the HRT.

The Thomas model was applied to the experimental data(continuous line, nonlinear (NL) model and dashed line,linear model, in Figure 1). A linear plot of ln[(C0/C) − 1]versus Ve to data located in the range 0.05 < /C0 < 0.90allowed a previous determination of the kinetic coefficient,Kt, and the adsorption capacity of the bed, q0, according toEquation (6). NL regression analysis was performed usingEquation (5). The sum of the squares of the errors (SSE) wasexamined for every experimental data set, and the parame-ters of Kt and q0 were determined for the lowest error valuesin each case by adjusting and optimizing the functions them-selves using the solver add-in for Microsoft Excel®. Thevalues of Kt and q0 obtained for the lowest error values aregiven in Table 1.

Except for copper, the Thomas model represented theflow rate data well. In general, the theoretical and experi-mental maximum adsorption capacities were closed. Theincrease in the flow rate resulted in an increase in theThomas rate constant and a decrease in the maximum

Dow

nloa

ded

by [

City

Col

lege

Lib

rary

] at

08:

41 0

3 M

arch

201

4

Environmental Technology 5

Figure 1. Comparison of experimental and theoretical breakthrough curves for metal ions at varied flow rates of (a) 100 mL min−1,(b) 200 mL min−1 and (c) 300 mL min−1 (NL, nonlinear; L, linear). Adapted from.[26]

adsorption capacity for metals studied with an initialmetal concentration of 200 mg L−1. According to Shahbaziet al.,[28] this occurs due to difference of metal ion radiussize as it passes through the column.

The NL regression analyses better represented the datathan linear (L) regression analyses. From Table 1, it can beseen that the errors for NL were lower than L, showing abetter fit.

Dow

nloa

ded

by [

City

Col

lege

Lib

rary

] at

08:

41 0

3 M

arch

201

4

6 G.S.C. Raulino et al.

Table 1. Parameters by linear (L) and NL regression analysis with Thomas model for metal ions Cu(II), Ni(II) and Zn(II) for the threeflow rates (CSWO treatment).

Kt (mL min−1 mg−1) q0 (mmol g−1) SSETheoretical

Metalion Flow rate (mL min−1) L NL L NL Experimental L NL

Cu(II) 100 0.102 0.113 0.242 0.242 0.233 0.061 1.36 E−29200 0.091 0.270 0.258 0.234 0.218 9.142 2.31 E−07300 0.292 0.299 0.191 0.180 0.172 0.428 1.69 E−29

Ni(II) 100 0.462 0.460 0.075 0.075 0.071 1.53 E−3 3.77 E−32200 1.008 1.141 0.096 0.091 0.093 0.357 4.44 E−31300 3.478 3.464 0.054 0.049 0.051 1.42 2.99 E−14

Zn(II) 100 0.412 0.410 0.075 0.075 0.071 3.35 E−4 1.17 E−28200 1.203 1.119 0.071 0.071 0.069 6.737 4.07 E−31300 2.716 1.991 0.057 0.050 0.050 1.059 6.84 E−13

Note: Adapted from.[26]

Table 2. EBCT and BUR for different bed heights.

Bed height EBCT Q BURMetalion (cm) (min) (mmol g−1) (g L−1)

Cu(II) 100 15 0.217 18.97160 24 0.264 13.63

Ni(II) 100 15 0.092 55.8160 24 0.111 53.1

Zn(II) 100 15 0.069 53.9160 24 0.075 46.15

Note: Adapted from.[26]

With the values of Kt and q0 for each metal, the totalmass of biosorbent required to treat wastewater in a col-umn can be obtained under the same conditions, requiringonly knowledge of the feed concentration for each metal,the daily flow rate and the volume of solution to betreated.

Applying the EBCT model and BUR (Equations (1) and(2), respectively) to the data obtained from the breakthroughcurves for bed height study resulted in the data shown inTable 2 and Figure 2(a). It can be seen that the breakthroughvolume for each metal and the adsorption capacity increasedwhile the BUR decreased with the increase in bed height.The BUR is lower for copper due to the effect of competitionbetween metal ions in solution and biosorbent sites. Thelower the BUR is, the greater is the adsorption capacity.

The literature reports that the greater the bed heightis, the greater the service time of the column because thesurface area of the biosorbent increases as the numberof active sites available for metal–biosorbent interactionincreases. The amount of biosorbent required to treat thesame volume of solution at the same concentration thereforedecreases.[19,29,30] The maximum HRT of 35 min [19] isnot exceeded when the column length increases from 100to 160 cm.

Figure 2(b) presents the critical bed depths (the bedheight when tb (breakthrough time) = 0) or the smallerbed depth to obtain an effluent concentration equals to Cb.

(a)

(b)

Figure 2. (a) BUR versus EBCT and (b) breakthrough timesversus bed heights.

The critical bed depth depends on the choice of Cb and isobtained by extrapolating the curve of breakthrough timeversus bed height to zero. The values of critical bed depthswere 40, 4 and-60 cm for copper, zinc and nickel, respec-tively. The negative value found for nickel means that, ina bed height greater than zero, it is possible to obtain aneffluent concentration Cb used in this work.[19]

3.3. Treatment influence on biosorbentThe results obtained with non-treated (CS) and treated CSoutside (CSWO, CSBO) and inside (CSWI, CSBI) the col-umn are shown in Figure 3. According to the results shown

Dow

nloa

ded

by [

City

Col

lege

Lib

rary

] at

08:

41 0

3 M

arch

201

4

Environmental Technology 7

Figure 3. Comparison of the treatments outside and insidecolumn for the three metal ions studied.

in Figure 3, the green CS treated with water (CSWO, CSWI)or NaOH (CSBO, CSBI) led to an increase in the adsorptioncapacity as well as the breakthrough and exhaustionvolumes, when compared with raw material (CS).

For the CSBO treatment, the adsorption capacityincreased about 40% for each metal ion when comparedwith the non-treated material (CS). This occurs becausewhen the lignocellulosic material is washed with NaOHsolution (0.1 mol L−1), the cellulosic fibre expands, andincreases the number of active sites available to improvingthe adsorption process.[8,9]

The increase in adsorption capacity was 27% for cop-per and zinc, while for nickel it was 37% when CSWOand CSWI treatments were compared. On the other hand,according to the results obtained for both treatments, out-side (CSBO) and in the column (CSBI), the use of greenCS powder treated with NaOH (0.1 mol L−1) increased theremoval percentage at 55.7% for copper, 58.9% for nickeland 73.7% for zinc from aqueous solution. However, theuse of this material for the same purpose without treatmentis also possible, with the potential for co-processing in otherindustrial sectors.

3.3.1. pH MonitoringThe pH, among several factors, can be regarded as the mostimportant parameter to influence the adsorption process. Inacid, there is an electrostatic repulsion between metal ionsand the biomass surface, enhancing the competition effect.In an alkaline medium, precipitation takes place with theformation of metal hydroxides. Moreover, depending on theconcentration of metal ions in solution, complexes can beformed, and other mechanisms can occur. On the other hand,the hydroxyl group increases the number of adsorption siteson the fibre surface, with interaction with metal ions mostlikely occurring.[15–17]

Figure 4(a) shows effluent solutions resulting frombiosorbent treatment in the column. With CSWI treatment,the pH of the effluent solution changes very little, remain-ing at approximately neutral. At the beginning of treatmentCSBI, the pH was acid even the feed solution has a basiccharacter, indicating that the sodium hydroxide influent is

(b)

(a)

Figure 4. pH-Curve of collected aliquots at the outlet of the col-umn filled with green CS powder (a) during treatments CSWI andCSBI and (b) from aliquots collected after percolating metallicsolution through the column.

interacting with the biosorbent in the column by modifyingits structure and morphology.[10,15,31,32]

After 6–7 L of basic solution, the pH starts to increase,indicating that an excess of basic solution has percolatedthrough the column. Then, 20 L of water was passed throughthe column to remove the excess basic solution, leaving thepH at approximately 13.

The pH of metallic effluent solutions that has beenpassed in experiments carried out to estimate the effectof the treatment outside and inside the column was mon-itored (Figure 4(b)). The pH remained almost constant inall three studies (CS, CSWO, CSBO) performed after treat-ment outside the column, suffering little decrease. For CSand CSWO treatments, the pH was approximately 5, andfor CSBO treatment, the pH was approximately 7. Thesedecreases may be due to ionic exchange between the biosor-bent surface and the solution, where the metal ion binds tothe fibre and releases H+ and the slightly acid (approxi-mately 4.5–6.0) character of the multi-component metallicsolution. Treatment with NaOH (0.1 mol L−1) showed bet-ter results, due not only to adsorption but also most likelyto the mechanisms of precipitation and complexation.[33]The use of hydroxides elevates the effluent pH to 7.0, leav-ing the effluent pH approximately neutral. In general, a lowinfluence on effluent pH was observed when the biosorbentwas treated outside the column.

Dow

nloa

ded

by [

City

Col

lege

Lib

rary

] at

08:

41 0

3 M

arch

201

4

8 G.S.C. Raulino et al.

Figure 5. COD curves for aliquots of collected effluent for CSWI and CSBI treatments.

After the treatments inside the column (CSWI andCSBI) were performed, a great decrease is observed whenthe metallic solution is passed, especially for CSBI treat-ment (Figure 4(b)). This may be due the excess of OH−available at the medium that is leached by the metallicsolution. The OH− ions available in the solution react withCu(II), Zn(II) and Ni(II) ions to form Cu(OH)2, Zn(OH)2and Ni(OH)2, respectively, although complexes such asCu(OH)2, CuOH+, NiOH+, Ni2OH3+, ZnOH+, Zn2OH3+can be formed.[3] After this great decrease, the samebehaviour for CSWO and CSBO is observed due to thesame reasons explained before.

3.3.2. Chemical oxygen demandFigure 5 shows that a maximum COD (approximately4900 mg L−1) was achieved when the biosorbent wastreated with NaOH (CSBI). Natural fibres such as green CSpowder contain high levels of lignin and cellulose. Whenthese cellulosic materials are subjected to a basic treat-ment, soluble phenolic compounds in the fibre are removed,resulting in the destruction of the lignocellulosic com-plex, solubilizing hemicelluloses and expanding fibrousmaterials, as well as extracting organic matter such astannins.[10,16,32,34] The high COD is the result of hydrox-ide action in the fibre, which removes large amounts oforganic matter. After percolation of the treatment solutionsthrough the column, the remaining COD was 60.3 mg L−1

for CSWI and 171.9 mg L−1 for CSBI.

3.4. Column adsorption in single- andmulti-component solutions

The breakthrough curves of the three metal ions studied insingle-component systems were prepared after optimization

Table 3. Comparison between adsorption capacities of greenCS powder submitted to treatment CSBI in multi- and sin-gle-component systems, when C/C0 = 0.5 (Fm = 200 ml min−1;C0 = 200 mg L−1).

Q (mmol g−1)

Metal ion CSBI multi-component CSBI single-component

Cu(II) 0.509 0.746Ni(II) 0.185 0.452Zn(II) 0.121 0.394

of the flow rate, bed height and biosorbent treatment.Table 3 shows the adsorption capacities of the biosorbent fortreatment CSBI in multi-component and single-componentsolutions, and can be observed that the adsorption capac-ity of each metal increased when passed from a multi-component to a single-component system, especially forzinc and nickel. This increase in adsorption capacity is dueto the effect of competition between metal ions for the activesites of the biosorbent. The results show that copper ionsare preferred by the sites over other ions studied becausethe increase in adsorption capacity of copper from a multi-component to a single-component system was lower thanthe other two ions, zinc and nickel as seen in Table 3.

3.5. Desorption of metal ionsIn the desorption of metal ions, 20 L of HNO3 (0.5 mol L−1)was used to elute these metal ions after CSBI treatment andcolumn saturation. After 20 L of acid solution percolatedthrough the column, the residual concentrations of metalions were 11 mg L−1 for copper, 4 mg L−1 for nickel and4 mg L−1 for zinc. Almost all of the copper was desorbed(98.54%), whereas only 50% of the nickel and zinc have

Dow

nloa

ded

by [

City

Col

lege

Lib

rary

] at

08:

41 0

3 M

arch

201

4

Environmental Technology 9

been desorbed, possibly due to desorption of nickel and zincions after saturation (C/C0 > 1) resulting from the compe-tition effect with copper for active sites. Sousa et al.,[35]studied the removal of metal ions using the green CS powdertreated with NaOH (0.1 mol L−1), verified that the biosor-bent can be used in only one cycle of adsorption under theseconditions because the efficiency of removal decreased afterthe second cycle. As the estimation of exhaustion volumefor copper was about 120 L, a reduction of 84% in thevolume is reached with desorption.

4. ConclusionsThe results indicated that the use of treated green CS powderis feasible for the removal of copper, nickel and zinc fromaqueous solutions.

With the increase in bed height, the adsorption capacityincreases and a smaller amount of biosorbent is required perlitre of solution to be treated. On the other hand, the increasein flow rate leads to a decrease in adsorption capacity.

Among the treatments both outside and in the column,the one with NaOH (0.1 mol L−1) on the column had thebest result, indicating an increase in pH and COD. Althoughthe use of green CS without treatment is possible, with thepotential for co-processing in other industrial sectors.

The adsorption capacity for a single-component solutionwas higher than that for a multi-component solution due tothe competition effect.

Supplemental dataSupplemental data for this article can be accessedhttp://dx.doi.org/10.1080/09593330.2014.880747.

References[1] Baird C. Química ambiental. Porto Alegre: Editora Book-

man;2002.[2] Sud D, Mahajan G, Kaur MP. Agricultural waste mate-

rial as potential biosorbent for sequestering heavy metalions from aqueous solutions – a review. Bioresour Technol.2008;99:6017–6027.

[3] Revathi M, Saravanan M, Chiya AB, Velan M. Removal ofcopper, nickel, and zinc ions from electroplating rinse water.Clean – Soil Air Water. 2012;40:66–79.

[4] Tarley CRT, Arruda MAZ. Biosorption of heavy metals usingrice milling by-products. Characterisation and applicationfor removal of metals from aqueous effluents. Chemosphere.2004;54:987–995.

[5] Ayoob S, Gupta AK, Bhakat PB. Analysis of breakthroughdevelopments and modeling of fixed bed adsorption systemfor As(V) removal from water by modified calcined bauxite(MCB). Sep Purif Technol. 2007;52:430–438.

[6] Suksabye P, Thiravetyan P. Cr(VI) adsorption from electro-plating plating wastewater by chemically modified coir pith.J Environ Manage. 2012;102:1–8.

[7] Huisman JL, Schouten G, Schultz C. Biologically producedsulphide for purification of process streams, effluent treat-ment and recovery of metals in the metal and mining industry.Hydrometallurgy. 2006;83:106–113.

[8] Bailey SE, Olin TJ, Bricka RM, Adrian D. A review ofpotentially lowcost sorbents for heavy metals. Water Res.1998;33:2469–2479.

[9] Gurgel LVA, Freitas RP, Gil LF. Adsorption of Cu(II),Cd(II), and Pb(II) from aqueous single metal solutionsby sugarcane bagasse and mercerized sugarcane bagassechemically modified with succinic anhydride. CarbohydrPolym. 2008;74:922–929.

[10] Brígida AIS, Rosa MF. Determinação do Teor de Taninos naCasca de Coco Verde (Cocos nucifera). Proc Interamer SocTrop Hort. 2003;47:25–27.

[11] Johnson PD, Watson MA, Brown J, Jefcoat IA. Peanut hullpellets as a single use sorbent for the capture of Cu(II) fromwastewater. Waste Manage. 2002;22:471–480.

[12] Singh KK, Hasan SH, Rastogi RJ, Removal of cadmium fromwastewater using agricultural waste rice polish. J HazardMater. 2005;A121:51–58.

[13] Kim JW, Sohn MH, Kim DS, Sohn SM, Know YS. Produc-tion of granular activated carbon from waste walnut shell andits adsorption characteristics for Cu2+ ion. J Hazard Mater2001;B85:301–315.

[14] Moreira SA, Sousa FW, Oliveira AG, Nascimento RF, BritoES. Remoção de Metais de Solução Aquosa Usando Bagaçode Caju. Quim Nova. 2009;32:1717–1722.

[15] Gurgel LVA, Júnior OK, Gil RPF, Gil LF. Adsorptionof Cu(II), Cd(II), and Pb(II) from aqueous single metalsolutions by cellulose and mercerized cellulose chemi-cally modified with succinic anhydride. Bioresour Technol.2008;99:3077–3083.

[16] Asadi F, Shariatmadari H, Mirghaffari N. Modification of ricehull and sawdust sorptive characteristics for remove heavymetals from synthetic solutions and wastewater. J HazardMater. 2007;154:451–458.

[17] Muhamad H, Doan H, Lohi A. Batch and continuous fixed-bed column biosorption of Cd2+ and Cu2+. Chem Eng J.2010;158:369–377.

[18] Sousa FW, Moreira SA, Oliveira AG, Cavalcante RM, Nasci-mento RF, Rosa MF. Uso da casaca de coco verde comobiosorbente na remoção de metais tóxicos. Quim Nova.2007;30:1153–1157.

[19] Cooney DO. Adsorption design for wastewater treatment.Boca Raton, FL: Editora CRC Press; 1999.

[20] Srivastava VC, Prasad B, Mishra IM, Mall ID, Swamy MM.Prediction of breakthrough curves for sorptive removal ofphenol by bagasse fly ash packed bed. Ind Eng Chem Res.2008;47:1603–1613.

[21] Yan G, Viraraghavan T. Heavy metal removal in a biosorp-tion column by immobilized M.rouxii biomass. BioresourTechnol. 2001;78:243–249.

[22] Vijayaraghavan K, Thilakavathi M, Palanivelu K, VelanM. Continuous sorption of copper and cobalt by crab shellparticles in a packed column. Environ Technol. 2005;26:267–276.

[23] Aksu Z, Gönen F. Biosorption of phenol by immobi-lized activated sludge in a continuous packed bed: predic-tion of breakthrough curves. Process Biochem. 2004;39:599–613.

[24] Rao M, Parwate AV, Bhole AG. Removal of Cr6+ and Ni2+from aqueous solution using bagasse and fly ash. WasteManage. 2002;22:821–830.

[25] Rosa MF, Abreu FAP, Furtado AAL, Brígido AKL, NorõesERV. Processo agroindustrial: obtenção de pó de cascade coco verde. Fortaleza: Embrapa Agroindústria Tropical;2001, 4 p (Comunicado Técnico, 61).

[26] Sousa Neto VO, Raulino GSC, Freire PTC, Araújo-SilvaMA, Nascimento RF. Equilibrium and kinetic studies in

Dow

nloa

ded

by [

City

Col

lege

Lib

rary

] at

08:

41 0

3 M

arch

201

4

10 G.S.C. Raulino et al.

adsorption of toxic metal ions for wastewater treatment.In: Naushad Mu, Alothman Zeid A, editors. A bookon ion exchange, adsorption and solvent extraction. 1ed. Hauppauge, NY: Nova Science publishers Inc; 2013.p. 145–182.

[27] Gao Z, Bandosz TJ, Zhao Z, Han M, Qiu J. Investigation offactors affecting adsorption of transition metals on oxidizedcarbon nanotubes. J Hazard Mater. 2009;167:357–365.

[28] Shahbazi A, Younesi H, Badiei A. Functionalized SBA-15mesoporous silica by melamine-based dendrimer amines foradsorptive characteristics of Pb(II), Cu(II) and Cd(II) heavymetal ions in batch and fixed bed column. Chem Eng J.2011;168:505–518.

[29] Han R, Zou W, Li H, Li Y, Shi, J. Copper(II) andlead(II) removal from aqueous solution in fixed-bed columnsby manganese oxide coated zeolite. J Hazard Mater.2006;B137:934–942.

[30] Malkoc E, Nuhoglu Y. Fixed bed studies for the sorptionof chormium (VI) onto tea factory waste. Chem Eng Sci.2006;61:4363–4372.

[31] Gurgel LVA, Gil LF. Adsorption of Cu(II), Cd(II), andPb(II) from aqueous single metal solutions by succinylatedmercerized cellulose modified with triethylenetetramine.Carbohydr Polym. 2009;77:142–149.

[32] Gu H. Tensile behaviours of the coir fibre and relatedcomposites after NaOH treatment. Mater Des 2009;30:3931–3934.

[33] Naja g, volesky b. Behavior of the mass transfer zonein a biosorption column. Environ Sci Technol. 2006;40:3996–4003.

[34] Filho JMP, Vieira EL, Silva AMA, Cezar MF, AmorimFU. Efeito do Tratamento com Hidróxido de Sódio sobre aFração Fibrosa, Digestibilidade e Tanino do Feno de Jurema-Preta (Mimosa tenuiflora. Wild). Rev Brasil Zootecnia.2003;32:70–76.

[35] Sousa FW, Oliveira AG, Ribeiro JP, Rosa FM, KeukeleireD, Nascimento RF. Green coconut shells applied asbiosorbent for removal of toxic metal ions using fixed-bed column technology. J Environ Manag. 2010;91:1634–1640.

Dow

nloa

ded

by [

City

Col

lege

Lib

rary

] at

08:

41 0

3 M

arch

201

4