The ability of coconut husk to remove methylene blue from solution was investigated. Factors such as initial dye

concentration, contact time, adsorbent dosage and pH of solution were studied. Results show that Langmuir

isotherm can be successfully applied to the methylede blue - coconut husk system and that coconut husk is a

suitable adsorbent for such a dye. Maximum adsorption capacity is 99 mg gl moss as derived from Langmuir

isotherm. A series of fixed bed experiments was carried out and the results were applied to a bed-depth/service time

model for column adsorption. The validity of such a model is discussed

Lee, C. K.

Low, K. S.

Universiti Putra Malaysia Institutional Repository

Pertanika 13(2), 221-228 (1990)The Removal of Cationic Dyes Using Coconut Husk as an AdsorbentK.S. LOW and c.K. LEEDepartment of Chemistry, Faculty ofAgricultureUniversiti Pertanian Malaysia.43400 UPM, Serdang, Selangor Darul Ehsan, MalaysiaKey words: adsorption, coconut husk, methylene blue, BDST model.ABSTRAK.Eksperimen tentang penggunaan sabut kelapa sebagai satu penjerap bagi metilena biru telah dijalankan.Parameter yang dikaji termasuk kepekatan larutan pewama masa tindakan, dos penjerap dan pH larutan.Keputusan menunjukkan bahawa isoterma Langmuit boleh digunakan pada sistem metilena biru - sabutkelapa. Di samping itu sabut kelapa adalah suatu bahan penjerap yang sesuai bagi metilena biru. Satu sirieksperimen mengenai padatan tetap telah dilakukan dan keputusan yang didapati dibandingkan dengansuatu model tinggi padatan/masa servis untuk penjerapan turus. Kesahan model ini juga dibincangkan.ABSTRACTThe ability of coconut husk to remove methylene blue from solution was investigated. Factors such as initial dyeconcentration, contact time, adsorbent dosage and pH of solution were studied. Results show that Langmuirisotherm can be successfully applied to the methylede blue - coconut husk system and that coconut husk is asuitable adsorbent for such a dye. Maximum adsorption capacity is 99 mg gl moss as derived from Langmuirisotherm. A series offixed bed experiments was carried out and the results were applied to a bed-depth/service timemodelfor column adsorption. The validity ofsuch a model is discussed.INTRODUCTIONThe discharge of colour materials fromindustrial wastewaters into streams and riversconstitutes one of the major sources of waterpollution. Owing to its colour, it is the mosteasily recognisable pollutant. Although it maybe present in minute quautities, its presenceis still clearly undesirable from the aestheticpoint of view. The treatment of dyes inindustrial wastewaters poses several problemsas the dyes are generally stable to light andoxidation and hence they cannot be treatedby conventional methods of aerobic digestion.The adsorption process provides anattractive alternative especially if the adsorbentis inexpensive and readily available. The useof activated carbon for treatment of coloureffluents has been investigated extensively(Molvar 1970; McKay, 1982). Fullers earth andbauxite have also been reported to besuccessful in removing colour on a laboratoryscale (Pearson 1913; Thorton and Moore,1953).Recently the use of low cost materials toremove colour has been reported by severalworkers. Poots and co-workers found that peatand wood can be successfully used to removeacid and basic dyes (1976, 1978). The sorptionof ionic dyes on wool carbonizing waste wasreported to be feasible (Perineau, 1980). Theremoval of cationic dyes using natural mosseswas also reported by Lee (1987).Coconut husk, a byproduct of coconut, isbeing used for the production of charcoal, fueland brooms. According to the Department ofStatistical Malaysia (1985), Malaysia produceda total of 120,195,000 coconuts in 1984. As thehusk is readily available, we investigated thepotential of such a material in removing dyesfrom solution.KS. LOW AND C.K. LEEThe bulk of coconut husk is made up ofcellulose and lignin (60%) . The hydroxylgroups in these two polymeric substance pro-vide sites for adsorption of dyes. Preliminaryinvestigation showed that cationic dyes likeAstrazone Red GTLN, Astrazone Pink FG,Astrazone Blue BG and methylene blue couldbe readily adsorbed on the husk. However,neutral dyes like methyl blue orange andphenol red showed no such activity.In this paper, the adsorption characteristicsof methylene blue-coconut husk system on alaboratory scale has been investigated.Parameters studied included adsorptiveequilibria as function of concentration, dosageand pH. A series of fixed bed experiments wasalso undertaken and the results were appliedto a bed-depth/service time (BDST) model forcolumn adsorption. (Hutchins 1973).MATERIALS AND METHODSSample PreparationCoconut husks collected from a nearby estatewere dried at room temperature. Afterremoving the outer layer, the husk was groundand then treated with a mixture offormalehyde/HCI according to the method ofRandall (1978) for the treatment of peanutshell. It was then sieved in succession intovarious fractions after drying at 80°C. Thelargest fraction (55% by weight) of size300-85011 was used in all the experiments.Methylene blue of 82% purity (British DrugHouse) was used without further purification.Contact Time ExperimentsIn all contact-time experiments, except wherethe effect of dosage of adsorbent was studied,0.5 g of husk was shaken in 100 ml meythleneblue solutions of varied concentrations.Aliquots of 1 ml solution were withdrawn atregular intervals for the analysis of the dyeusing a Shimadzu UV-160 spectrophotometer.All· m~asurements were recorded at A 665. maxnm at room temperature.In· the study of the effect of adsorbentdosage on dye uptake, the weight of samplewas varied from 0.25 to 1.5 g while the dyeconcentration was maintained at 250 mg J-J.The effect of initial concentrations wasstudied by varying the dye concentration of thedye solution from 50-500 mg 1-1.The influence of pH was conducted underan equilibrium condition. The pH of thesolution was adjusted by dilute HCl or NaOHbefore experimentation. A contact time ofthree hours with constant shaking was main-tained. In order to eliminate the effect of pHon colour, all solutions were adjusted to thesame pH that is 5.20 before measurementswere recorded.The reproducibility of the experiments wasestablished by shaking four replicates of 100ml 500 mg J-l methylene blue solution with0.5 g coconut husk.Adsorption IsothermsAdsorption isotherms were obtained by shaking0.25 g of coconut husk with 100 ml of dyesolution for four hours. The concentration ofthe dye solution was varied from 250-1000 mg1-1.Fixed-bed StudyIn the flow studies, vertical glass columns ofinternal diameter of 2.2 cm were used. Thehusk was packed to a height of 3, 6, 12, 18 cmcorresponding to 0.625, 1.25, 2.50 and 3.75 gof samples respectively. Flow rate wascontrolled by means of a clip attached to thebottom of the column. Dye solution of 50 mg1-1 was passed through the column and 250ml-fraction were collected and analysed formethylene blue. The flow rate was variedbetween 25-75 ml min-I.RESULTS AND DISCUSSIONReproducibilityThe reproducibility of the experiments wasestablished by shaking four replicates of 100ml 500 mg J-l methylene blue solution with 0.5g coconut husk. The relative standard deviationwas found to be less than 4%.Effect of pHThe effect of pH on the uptake of methyleneblue by coconut husk is shown in Fig. 1. Theadsorption capacity increased with increasing222 PERTANlKA VOL. 13 NO.2, 1990THE REMOVAL OF CATIONIC DYES USING COCONUT HUSK AS AN ADSORBENTlUllIU80I;D-a. 40MDCIt-aC~ 202 6 8pH10 12 14100 --~80rip:. I: F///'I/u/ iuilifll /illu// /hl" fI/i/fll,,'u/ /l1/'/hyf"ul' (,f//I·.-~-20n(mg 1-)• 50o 100T 250o 500o 40 80 120 160Tim e200 240(m In)280 320 360Fig. 2: Effect of concentration on the uptake of rnethylene blue. Condition: U. 5 g husk/l OOml solution.pH. At pH 12, almost 100% adsorption wasachieved. This is attributed to the increasingelectronegative charge of the adsorbent as thepH of the solution increases. A similar observa-tion was also reported by Perineau and co-wor-kers (1980) in their study of dye uptake bywool carbonizing waste. However, subsequentexperiments were performed without adjustingthe natural pH of the solution, which was 5.20.Effect of Initial ConcentrationThe influence of initial concentration on thePERTANlKA VOL. 13 NO.2, 1990 223K.S. LOW AND C.K. LEE(mg rl• 250o 500adsorption of dye on coconut husk is shownin Fig. 2. The time taken to reach equilibriumincreased with increasing concentration. Foran initial dye concentrations of less than 100mg P, saturation was attained in less than 20minutes. This was increased to about threehours when the concentration reached 500 mg1-1. The initial rapid adsorption of dye couldbe attributed to ion-exchange with surface ca-tions on the husk followed by a gradual uptakewhich could be due to cation exchange at theinner surface. Poots and co-workers (1978) intheir study on removal of Astrazone Blue bywood, reported that initial concentration ofdye has very little influence on the time of con-tact to reach equilibrium. The reason for suchan observation is not clear. For a given massof adsorbent, the amount of dye it can adsorbis fixed. The higher the concentration of thedye, the smaller the volume it can remove.The kinetics of adsorption appears to befirst order. Plots of log C against time for 250and 500 ppm solutions for the first twentyminutes of contact time yielded straight lines(Fig. 3). No attempts were made to determinethe kinetics of solution with concentration lessthan 100 mg I-I as equilibrium time was toorapirl.2.00 5 10 J5 20 25Time (min)2-6~2·4~CD......2'2100--.-.V" • - •-•80cClI ( u)60 0a.• 0·25..ClI 0 0·50In 40"1:1 1·00c •~ 0 l' 5020 )0 6Q 120 180 UO 300 360TI rno (m In)Fig. 4: Effect ofadsorbent dosage on the uptake oj 1I/I'/llyll'l/l' !JI/ll'. Condition: IIlI 250 Ilg I-I methyl blue solution.224 PERTANlKA VOL. 13 NO.2, 1990THE REMOVAL OF CATIONIC DYES USING COCONUT HUSK AS AN ADSORBENT64'7lCII~Ct 3Neu:z 2"euUol..-----...------__--__--,. --.- ......l1 2Ce (x 10 mg ml"l)3 4 5Fig. 5: 1.11 I/glI/lIir iSIJ/hI'J"II }IJr lhl' "r!sOIjJ/iul/ u} II/l'ihY/I"/l' b//II' UII cucullul husk.Effect of Adsorbent DosageThe effect of the amount of adsorbent on theadsorption of a fixed quantity of methyleneblue is shown in Fig. 4. The rate of adsorptionand the percentage adsorption of the dyeincreased with increasing the amount of husk.This is due to the increase in binding sites inthe adsorbent,Adsorption IsothermThe results from adsorption studies atequilibrium can be used to determine themaximum of dye adsorbed by the husk by usinga modified Langmuir isotherm shown below(Zimdahl and Skogerboe 1972).CeCeNeN*b + N*where Neis the amount of dye adsorbed pergram of husk at concentration Ceo A plot ofC IN against C is shown in Fig. 5. Thec~effi~ientof corr;lation of such a plot is 0.996indicating the general validity of the equationwhen applied to the adsorption of dye oncoconut husk. The maximum adsorption of thesystem (N*) is 99 mg g-l. This comparesfavourably with the experimental value of 102mg g-l. In a similar study using natural mossas an adsorbent, a value of 252 mg gl wasreported by Lee and Low (1987). Despite itslower adsorptive power, coconut husk, a cheapagricultural by product, could still be used toremove methylene blue from wastewaters.Column StudyAdsorption isotherms are useful in providinginformation on the effectiveness of theadsorption system. However, the isotherms areobtained under equilibrium conditions. Inmost industrial treatment applications, the con-tact time is not suffciently long for equilibriumto be achieved. In order to establish thesuitablity of coconut husk in removingmethylene blue on a continuous basis, someflow studies using columns were conducted.For column operation, the husk is in constantcontact with a fresh solution and henceequilibrium is unlikely to be attained. Theusefulness of a column is related to the lengthof time before renewal or regeneration is.necessary. For this purpose, the determinationof breakthrough curve at different bed depthsand flow rates is necessary. Fig. 6 shows a seriesPERTANlKA VOL. 13 NO.2, 1990 225K.S. LOW AND C.K. LEEu 50mlmln o \H(em)100 • 3!:>. 6• 1280 o 18c:: 60D-Do...D 40'"'aC~200 6 12Volume•18 24eluted (x 250ml)30 36Fig. 6: Ihmk/hrough ("unli's jor dijJi'I'PIl/ "{'(I-dpll/h.1 of ({)I"OI/ (1/ husk at a constant flow rate of50 ml min'l.204 8 12 16Volume eluted (x250m1JFig. 7: Breakthrough curves for different flow rates at a fixed bed depth of 6 em.o100 Bed- depth I 6 emu I ml mln"l,80 • 25c:: A 50D- 80 • 75-Do...•III'a 40c~20of breakthrough curves at different bed heights(H) of coconut husk at a flow rate (u) of 550ml min'!. Other flow rates of 25 and 75 ml min'I show similar trends of breakthrough curves.For a small bed mass which is proportionalto the bed height, the 50% breakthrough risesrapidly and this breakthrough time (tl / 2 )becomes larger with increasing mass. Reducingthe flow rate increases the volume of dye.treated before 50% breakthrough occurs. Thisis illustrated in Fig. 7 where the height wasfixed at 6 cm and the flow rates varied from226 PERTANlKA VOL. 13 NO.2, 1990THE REMOVAL OF CATIONIC DYES USING COCONUT HUSK AS AN ADSORBENTFig. 8: l~.\j)l'rillll'lll{//II/II/III/W/II/Nt JjJJ.\F (JII'; brmk-through) curves for diJferent flow rates.CONCLUSIONThe study shows that coconut husk, a cheap68Calculated Variation(t1/ 2) (%)I7.9x-3.67 I8.8x-7.099.4 x -7.095.8 x -6.04 6.3 x -7.09Bed-depth (em)Experimental(t1/ 2)255075-- ExlIerlmen tal18---- CalculatedIS 11 (1111 min-I)/.2514-. 5001512c: 10EQ"" 8,.:-(1).,1.. 6e'" 4..,::.,'"23 6 12 15 18TABLE 1Experimental and calculated BDST equations forflow rates based on u = 50 ml min- Isaturated. This is especially so if the adsorbentis expensive. However, in this case, coconuthusk is a cheap agricultural byproduct. It canbe burned with the adsorbed dyes and usedas a source of energy.The slope a of the line is the time requiredto exhaust the lenght of the fixed bed undertrial conditions, or the time required for thewave front to move through 1 cm of the bed.The intercept of the abscissa is the critical beddepth xo' defined as the minimum depth formaintaining satisfactory effluent at time zerounder the trial conditions. The ordinateintercept, b, is a measure of the adsorptionrate and is defined as the time required forthe adsorption wave front to pass through thecritical bed depth. Plots of BDST at 50%adsorption against bed-depth at various flowrates are shown in Fig. 8. The plots are linearindicating the general validity of the model.Mter obtaining a BDST equation from columnstudies for one particular flow rate, theequations for the other flow rates can becalculated. Using a flow rate of 50 ml min-1 asa reference, equations for 25 and 75 ml min-1were calculated and shown in Table 1.Variation between calculated andexperimental values are less than 10%,indicating that the BDST model could besatisfactorily applied to the methylene blue-coconut husk system.In most treatment processes for theremoval of dyes, it is necessary to regenerateand reuse the adsorbent once it becomeswhereservice time at breakthrough, mina slope = (No/Cov), min cm- Ib ordinate intercept = I/(kC)ln(Co/C-I), minNo adsorption capacity, mg adsorbate per cm3adsorbentCo initial concentration of methylene blue mg1-1v linear flow rate ml min-! cm-2k rate constant fo adsorption I mg-! min-!C eluant concentration mg I-I25 to 75 ml min-I.The results obtained from the break-through curves are applied to a bed-depth/service time model as proposed by Hutchins(1973). It predicts the service time of a columnwih operation variables. The equation of sucha model is given below:t=ax+bPERTANIKA VOL. 13 NO.2, 1990 227K.S. LOW AND C.K. LEEand easily available agricultural by product, canbe effectively used to remove methylene bluefrom solution. Results of the column studiesshow that the rate at which the husk has to bereplaced once it is saturated with the dye, canbe predicted quite satisfactorily by theHutchins BDST model.REFERENCESDAVIS, R.A, J.K. HAR!\1UT and M.M. CLEMEUS. 1973.Removal of Organic Material by AdsorptionActivated Carbon. Chern and Ind. (G.B.) 1:827.HUTCHINS, R.A. 1973. New Method Simplifies Designof Activated Carbon System. Chem. Engng. 80:133-138.5LEE, C.K. and K.S. Low. 1987. The Removal ofCationic Dyes by a Natural Moss. Part 1. Adsorp-tion Studies. Pertanika. 10(3): 327-334.McKAY, G. 1982. Adsorption of Dyestuffs fromAqueous Solution with Activated Carbon II:Column Studies and Simplified Design Models.j. Chem. Tech. Biotechnol. 32:773-780.MOLVAR, A.E. 1970. Treating Textile Waste withActivated Carbon. Textile Chemists and Colourists.2:36.PERINEAU, F.J. MOLINIER andJ. GASET, 1983. Adsorp-tion of Ionic Dyes on Wool Carbonizing Waste.Water Res. 17(5): 559-567.PEARSON, C.L. 1913. Fullers Earth Min. Techno!., 3,Bull. 71, U.S. Bureau of Mines.POOTS, V JP., G. McKAY and JJ HEALY, 1976. TheRemoval of Acid Dye from Effluent UsingNatural Adsorbents. I Peat. Water Res. 10:1061-1066.POOTS, VJP., G. McKAY andJJ HEALY. 1976. TheRemoval of Acid Dye from Effluent UsingNatural Adsorbents. II Wood. Water Res. 10: 1067-1070.POOTS, VJP., G. McKAY and JJ HEALY. 1978.Removal of Basic Dye from Effluent Using Woodas an Adsorbent. Journal TM'Q'. May: 926-935.RANDALL, J.M., E. HANTELLA and AG. WAlss. 1978.Binding of Heavy Metal Ions by FormaldehydePolymerised Peanut Skins. j. Anal. Polyrn. Sci.22:379-89.THOR!.'\'TON, H.A. and J.A MORE. 1953. Adsorbentin Wastewater Treatment - Dye Adsorption andRecovery Studies. Ind. Waste. 23:497.ZIMDAHL, R. and R. SKOGERBOE. 1972. Behaviour ofLead in Soils. Enviro. Sci Tech. 13:1202-1209.(Received 28 July, 1989)228 PERTANlKA VOL. 13 NO.2, 1990

The Removal of Cationic Dyes Using Coconut Husk as an Adsorbent

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The Removal of Cationic Dyes Using Coconut Husk as an Adsorbent

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