Lalit Sharma , 2 · 1 Lalit Sharma , 2 Subhash Chander Sharma Address For correspondence: 1, 2 PTU Regional Centre for PG studies (Environmental Science & Engineering), Shaheed

International Journal of Applied Research & Studies ISSN 2278 – 9480

iJARS/ Vol. II/ Issue 2/Feb, 2013/342 1

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Research Article

Tween 20 modified sugarcane bagasse (saccharum officinarum) and sheesham sawdust (dalbergia sissoo) for Cr(VI) remediation in aqueous environment

Authors:

1 Lalit Sharma *, 2

Subhash Chander Sharma

Address For correspondence:

1, 2 PTU Regional Centre for PG studies (Environmental Science & Engineering), Shaheed Bhagat

Singh State Technical Campus, Ferozepur – India).

Abstract

The adsorption of Cr (VI) was examined in aqueous solution onto plant based biosorbents viz. sugarcane

bagasse (saccharum officinarum) and sheesham sawdust (dalbergia sissoo) and their surfactant (Tween-

20) modified forms. Effects of various process parameters such as contact time, adsorbent dosage, pH

and metal concentration were investigated. The adsorption capacities of the biosorbents were found

dependent on the pH of Cr(VI) solution, with pH 2.0 being optimal. Surfactant modified biomass were

found better biosorbents compared to raw form. The adsorption capacities were found to be 71.4 mg/g,

67.1 mg/g, 40.7 mg/g and 37.3 mg/g for surfactant modified dalbergia sissoo, raw dalbergia sissoo,

surfactant modified saccharum officinarum and raw saccharum officinarum, respectively. The linear

Langmuir model fitted well to describe equilibrium isotherms.

Keywords: Water Pollution, biosorbents, Tween-20, plant based biomass, Cr(VI), isotherms.

Introduction

Chromium (VI) is a known human carcinogen and is one of the hazardous heavy metal that has been a

major focus in water and waste water treatment. In order to remove Cr(VI) from aqueous solution,

different methods are available e.g. chemical precipitation, lime coagulation, ion-exchange, reverse

osmosis, solvent extraction and biosorption etc. Whereas other methods are expensive and time-

consuming and often, more than one method is necessary to optimize the uptake effort, biosorption1,2 is a cost effective and

simple separation process as it utilizes inexpensive non living agriculture biomass and is particular useful for the removal of

heavy metal ions from waste water. As it is considered as environmentally benign emerging technology these days, it is

worthy to mention that an early attempt at bisorption was reported by Adams and Holmes in 19353.

[email protected] * Corresponding Author Email-Id

mailto:[email protected]



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In the last decade, a number of studies4-27

has demonstrated the feasibility of using plant based

adsorbents to remove heavy metals from waste water. Studies28-34

has also been reported using

chemically modified biomass to remove heavy metals from waste water. The purpose of present study is

to explore the potential of local plant based biosorbents viz. saccharum officinarum and dalbergia sissoo and their chemically

(Tween-20) modified forms for Cr(VI) remediation from aqueous solutions. The studies revealed that the modification of

biomass with Tween-20 (polyoxyethylenesorbitan monolaurate), a non-ionic surfactant, influenced/increased the adsorption

capacities of raw biomass up to 9.1%. Desorption studies were also performed and revealed the possibility of the recycling

of adsorbents and adsorbates.

Materials and Methods

Reagents and biosorbents

All the reagents used were of analytical grade and triply distilled water was used for all studies. The

plant based biosorbents were obtained from the local area. Materials were boiled with distilled water for

30 min. and washed thoroughly with distilled water, filtered, dried in air followed by oven drying at

120oC for 24 h. After pulverization the particle size was maintained below 180 microns and adsorbent

was kept in a dry container.

Modification of biosorbents

Biosorbent (100g/L) from above was soaked in Tween-20 aqueous solution (1g/L) for overnight and

shaken for 6 hrs on a vortex shaker at 160 rpm. After filtration, biomass was washed with doubly

distilled water and dried in hot air oven at 800C for 24 h. After cooling to room temperature in a

desiccator, it was kept in an air tight container.

Preparation of Cr(VI) solution

An aqueous stock solution (1000 mg/L) of Cr(VI) ions was prepared using potassium dichromate salt

and was used as a source of Cr(VI) in synthetic waste water. The pH of the solution was adjusted using

0.2 N H2SO4 or NaOH solution.

Batch sorption experiments

All adsorption experiments were carried out at pH 2.0 using 100 ml of Cr(VI) solution of desired

concentration (20 mg/L) and adsorbent (2g/100 ML) in a 250 mL Erlenmeyer flask at room temperature.

After agitation (160 rpm), the solution was filtered through Whatmann’s Filter paper no.1. Fourier

Transform Infrared spectra of the biomass samples were obtained using a Thermo Nicolet 6700 FT-IR

Spectrophotometer. Powdered samples were pelleted with KBr. The Cr(VI) concentration in filtrate was

estimated at 540 nm by 1-5-diphenylcarbazide method35

.



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Results and Discussion

Comparative performance of Tween 20 modified and raw biosorbents for the removal of Cr(VI)

The present studies revealed that Tween 20 treated biomass, compared to raw biomass, exhibited an

approximate 6.4% and 9.1% enhancement in total Cr removal for dalbergia sissoo and saccharum

officinarum, respectively. In the FT-IR spectra, peaks for dalbergia sissoo were found at (cmˉ1): 3400

(OH), 2932 (CH2), 1740 (C=O, ester), 1631 (C=C), 1463 (CH2, bending vib.), 1033 ( cellulose linkages)

and for saccharum officinarum IR peaks were found at 3421 (OH), 2922 (C-H), 1736 (C=O), 1632

(C=C), 1455 and 1047 (cellulose linkages). The FTIR of the modified biomasses indicated enhancement

at 3200-3600 cmˉ1 and 990-1230 cmˉ

1 for dalbergia sissoo and at 3150-3650 cmˉ

1 and 990- 1300 cmˉ

1

for saccharum officinarum, suggesting increased –OH and cellulose linkages. Additional peaks in

surfactant treated biomass at 2095-2295 cmˉ1

were assigned to protonated nitrogen containing

compounds. It was also reported 36

that ethylene oxide containing surfactants and polymers bonded with

lignin by hydrophobic interactions and hydrogen bonding reduce unproductive binding of enzymes.

Thus applying surfactants could modify the surface properties of lignin removing on pretreated solids

and improve cellulose effectiveness and accessibility to the surface. Hence coating plant based biomass

with non-ionic surfactant Tween 20 might expose more metal binding sites and improve the adsorption

property.

Effect of pH on Cr(VI) adsorption

The pH of the aqueous solution is an important parameter that controls the biosorption process. The

effect of pH on the biosorption of Cr(VI) onto the biosorbents viz. saccharum officinarum, dalbergia

sissoo and their surfactant (Tween-20) modified forms was determined by conducting batch sorption

studies at pH 2.0 to 7.0. The maximum adsorption of chromium was 95.9%, 86%, for dalbergia sissoo

and saccharum officinarum, and 99.6%, 95.15% for coated dalbergia sissoo and saccharum officinarum

at pH 2.0. There was a sharp decline in the percent adsorption with increase in pH of the aqueous

solution. Chromium adsorption at pH 2.0 and pH 7.0 corresponding uptake yield values were found to

be 95.9% and 20.20% for dalbergia sissoo, 99.62% and 28% for coated dalbergia sissoo, 86% and

11.3% for saccharum officinarum, and 95.2 % and 12.5% for coated saccharum officinarum,.

So, the maximum uptake of Cr (VI) was recorded for coated delbergia sisso at pH 2.0, which

decreases with further increase in pH. Hence pH 2.0 was taken as the optimal pH value for adsorption

experiments. The results are consistent with other workers10, 11

. The removal of Cr (VI) decrease with

increase of pH >4. The pH dependence of metal adsorption can largely be related to the type and ionic

state of functional groups present on the adsorbents and the metal chemistry in solution7. At lower pH

the maximum adsorption is take place due to an increase in H+ ions on the adsorbent surface resulting in

significantly strong electrostatic attractions between positively charged adsorbents surface and Chromate



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ions6, 8

. A sharp decrease in adsorption above pH 3.0 may be due to occupational adsorption sites by

anionic species like HCrO4-, Cr2O7

2-, CrO4

2- etc. which retard the approval of such ions further towards

the sorbent surface25

. At higher pH values the decrease in adsorption may be due to duel competition of

both the anion (CrO42─

and OH─) to be adsorbed on the surface of the adsorbent of which OH

─

predominates. It was postulated that under acidic conditions Cr (VI) could be reduced to Cr (III) in the

presence of an adsorbents. However in basic condition it is much less oxidizing and exists as Cr (OH) 3.

So, the reason for higher adsorption in acidic pH range is the oxidation of Cr2O72-

ions to Cr3+

, which

gets easily replaced by positively charged spicies. These results indicate that pH affects the solubility of

metals and the ionization state of the functional groups of the biosorbents26

.

Figure- 1: Effect of pH on biosorption of Chromium (VI), Initial Cr (VI) conc. = 20mg/L Biosorbents

dosage = 2g/ 100ml, Contact time =2 hrs.

Effects of contact time on chromium adsorption

Contact time is one of the effective factors in batch adsorption process. In this stage all the parameters

except contact time, including temperature (200C), adsorbent dosage 2g/100ml, pH 2.0, initial

concentration 20mg/l and agitation speed 160rpm were kept constant. The equilibrium time required for

the biosorption of Cr (VI) on dalbergia sissoo and saccharum officinarum and coated dalbergia sissoo

and saccharum officinarum with 2g/100ml of the biosorbents at different time intervals were studied.

(2a)



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(2b)

Figure-2(a and b): Effect of contact time on biosorption of Cr (Vl) ; Initial Cr (VI) conc. = 20mg/l, pH

2, Biosorbents dosage = 2g/100ml.

Figure 2 indicated that adsorption capacity sharply increases with increase in time and attain

equilibrium in 20minutes for dalbergia sissoo and 15 minutes for coated dalbergia sissoo, 100 minutes

for saccharum officinarum, and coated saccharum officinarum, respectively. The removal rate of Cr (VI)

increase with increase of the adsorption time. However, it remains constant after an equilibrium time

which indicated that the adsorption tends towards saturation. Therefore the adsorption time was set to

120 minutes for each experiment. The rate of adsorption is higher, initially due to large available

surface area of biosorbents. After the capacity of the adsorbent gets exhausted i.e. at saturation. The rate

of uptake is controlled by the rate at which the adsorbate is transported from external to the internal sites

of the biosorbents particles21

.

Effect of adsorbent dose on Chromium adsorption: -

The percent adsorption of Cr (VI) on different adsorbents was studied at different adsorbent dosage i.e.

2.5g/L, 5.0g/L, 10.0g/L, 15.0g/L and 20.0g/L, respectively. The equilibrium time was 2hrs, conc. of

chromium 20mg/L, pH 2.0 and agitation speed was 160rpm at room temp 200 C. All the conditions

except dosage were kept constant.

Figure-3: Effect of biomass dosage on biosorption of Cr (VI) : Initial Cr (VI) conc. = 20 mg/L; pH

2.0; Contact time = 2hrs.



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Figure-3, indicated that most of the chromium removal by coated dalbergia sissoo 99.6%, (15minutes)

and dalbergia sissoo 95.4%, (20 minutes) coated saccharum officinarum, 95.15% and saccharum

officinarum 86%, achieved in 100 minutes. So, experiments were conducted at 100 minutes. The results

revealed that with increase in the adsorption dose, percentage adsorption of chromium was increased

(Fig. -3) and the maximum removal was observed with adsorbent dosage of 20g/L of coated dalbergia

sissoo , dalbergia sissoo and coated saccharum officinarum, saccharum officinarum, respectively.

Increase in the percentage adsorption with adsorbent doses may be due to the increase in adsorbent

surface area and availability of more adsorption sites 37

. More quantity of biosorbents results in

increasing of surface area and biosorption regions which cause removal of more chromium. The

decrease in Cr (VI) uptake at higher adsorbent dose (Table 1) may be due to overlapping of adsorption

sites as a result of overcrowding of adsorbent particles38

.

Table-1: Adsorption capacity of different adsorbents at different adsorbent doses

Adsorbent dose

(g/L)

Saccharum

officinarum

qe (mg/g)

Modified

saccharum

officinarum

qe (mg/g)

Dalbergia sissoo

qe (mg/g)

Modified

dalbergia

sissoo

qe (mg/g)

2.5 1.68 1.94 2.83 3.26

5.0 1.14 1.22 2.62 2.77

10.0 1.12 1.19 1.89 1.95

15.0 0.87 0.99 1.27 1.33

20.0 0.86 0.95 0.96 1.00

Effect of initial chromium concentration on adsorption process:-

Initial concentration is one of the effective factors on adsorption efficiency. The experiments were done

with variable initial chromium conc. 20mg/L, 40mg/L, 60mg/L, 80mg/L, 100mg/L and constant temp

200C , pH 2.0, agitation speed 160rpm, contact time 2hrs and 2g of adsorbent dosage(2g/100ml).

Experimental results of effect of initial chromium conc. on removal efficiency were presented in Figure-

4. Chromium removal efficiency decreased with the increased in initial chromium concentration but the

amount of chromium adsorbed per unit mass of adsorbent was increased with increased in chromium

conc. in the test solution. As the chromium conc. in the test solution was increased from 20mg/L to 100

mg/L the unit adsorption of chromium on biosorbents increased (Table 2). The adsorption capacity of

an adsorbent which is obtained from the mass balance on the sorbate in the system was solution volume

V is often used to acquire the adsorption isotherms under the experimental condition. The amount of

adsorbed Cr(VI) ions per gram biomass is obtained by using the following equation:



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qe = (C0 – Ce) V ……………. (1)

m

where, qe is the amount of Cr(VI) ions adsorbed on the biomass (mg/g), Co (mg/L) is the initial

concentration of Cr(VI) in solution, Ce (mg/L) is the concentration of Cr(VI) at equilibrium, V is the

volume of medium (L) and m is the mass of the adsorbent (g).

Figure- 4: Effect of Initial metal concentration on biosorption of chromium (VI); Biosorbents dosage =

2g/100ml, pH 2, contact time = 2hrs.

Table 2: Adsorption capacity of different adsorbents at different initial Cr concentration

Cr(VI) conc.

(mg/L)

Saccharum

officinarum

qe (mg/g)

Modified

saccharum

officinarum

qe (mg/g)

Dalbergia

sassoo

qe (mg/g)

Modified

dalbergia

sassoo

qe (mg/g)

20 0.86 0.95 0.96 0.99

40 1.23 1.47 1.79 1.91

60 1.55 1.69 2.46 2.62

80 1.58 1.91 2.79 2.98

100 1.77 1.95 3.18 3.51



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Adsorption Isotherms

The Chromium uptake capacity of coated dalbergia sissoo , dalbergia sissoo and coated saccharum

officinarum, saccharum officinarum were evaluated using the Langmuir39

and Freundlich40

adsorption

isotherms.

The Langmuir equation which is valid for monolayer sorption onto a surface with a finite number of

identical sites which are homogeneously distributed over the adsorbent surface is given by equation.

qeq = qmaxbCeq ………….. (2)

1+ bCeq

Where qeq is the amount of metal ions bound to per g of the dried biomass at equilibrium and Ceq is the

residual (equilibrium) metal ions concentration left in the solution after binding respectively. qmax is the

maximum amount of metal ions per unit weight of sorbent to form a complete monolayer on the surface

and b is a constant related to the affinity of qmax . The binding sites qmax and b can be determined from

Ceq/qeq versus Ceq plot which gives a straight line of slope 1/qmax and intercept 1/bqmax.

The Freundlich equation is an empirical equation based on adsorption on a heterogeneous surface.

This equation proposes a monolayer sorption with a heterogeneous energetic distribution of active sites

accompanied by interactions between adsorbed molecules. The general from of equation is :

qeq = KfCeq1/ n

……………. (3)

Where eeq is the equilibrium concentration mg/L, qeq is the amount of metal ion bound to per

gram of the dried biomass at equilibrium (mg/g) and Kf, n are the Freundlich constants related to

sorption capacity and sorption intensity of the sorbent, respectively. The equation 2 can be linearized in

logarithmic form and Freundlich constants can be determined.

log qeq = log Kf + 1/ n log Ceq …………….. (4)

The value of Kf (mg g-1

) can be taken as a relative indicator of sorption capacity, while 1/n shows the

energy or intensity of sorption. The Langmuir and Freundlich adsorption isotherms are presented in

Figures 5 and 6. The maximum value of qm determined is 71.42 mg g-1

(Table 3) for chromium

adsorption using Tween 20 modified dalbergia sissoo.

Table 3: Langmuir and Freundlich isotherms

S.No.

Biomass

Langmuir

isotherm

Freundlich

isotherm

ka

(L mg-1)

qmax

(mg g) -

1

R2 logkf n R2

1. Saccharum

officinarum

0.168 37.31 0.9892 1.121 4.26 0.9791

2. Modified

saccharum

officinarum

0.327 40.65 0.9956 1.289 5.76 0.9968

3. Dalbergia sissoo 0.304 67.11 0.9927 1.328 3.16 0.9827

4. Modified

dalbergia sissoo

0.690 71.42 0.9860 1.525 4.71 0.9958



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(5 a)

(5 b)

(5 c)



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(5 d)

Figure- 5: (a, b, c, d) Langmuir Plot for Adsorption of Cr(VI) by saccharum officinarum, dalbergia

sassoo, Tween-20 modified saccharum officinarum and Tween-20 modified dalbergia sassoo.

In addition to Langmuir adsorption isotherm, the fitting of data to Freundlich sorption isotherm reveals

that the sorption process is not restricted to one specific class of sites and assumes surface heterogeneity.

But the Langmuir model gave the best fitting of the experimental results.

(6 a)

(6 b)



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(6 c)

(6 d)

Figure-6. Freundlich Isotherm (a - d) for saccharum officinarum, dalbergia sissoo, Tween-20 modified

saccharum officinarum and Tween-20 modified dalbergia sassoo.

The adsorption on to the plant based biomass used as biosorbents in the present investigation were

modeled. The values of the Langmuir constant(qm , Ka) and Freundlich constants ( Kf, n) are documented

for biosorption of hexavalent chromium by Saccharum officinarum, modified Saccharum officinarum,

dalbergia sissoo and modified dalbergia sissoo, respectively (Table-5). . Figure -5 and Figure-6 show

the Langmuir and Freundlich isotherm model of chromium (VI). It was found that coated dalbergia

sissoo had maximam metal uptake capacity of 71.42mg/g when compared to other biomass .The

regression constants are listed in table-5. The value of correlation coefficient R2=0.9958 showed that

the data conform well to the Freundlich equation although the strength of relat ionship between

parameters is not good as in case of Langmuir equation. On the basis of the datas of table -5 it is clear

that Coated Sesham Sawdust is the best adsorbent and fitted well for Langmuir isotherms.



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Conclusion:

The results revealed that surfactant coated biomass have better biosorption capacities compared to raw

forms. The biosorption capacities were found to be 71.4 mg/g, 67.1 mg/g, 40.7 mg/g and 37.3 mg/g for

surfactant modified dalbergia sissoo, raw dalbergia sissoo, surfactant modified saccharum officinarum

and raw saccharum officinarum, respectively. Thus surfactant coating could modify the surface

properties of the biomass for better Cr(VI) removal. The chromium removal was highly dependent on

pH, initial chromium concentration adsorbent mass and contact time. The pH 2.0 was found optimal for

maximum adsorption of chromium metal by all used adsorbents. The Freundlich and Langmuir

biosorption models were used for the mathematical description of the biosorption equilibrium of Cr(VI)

ions to biosorbents. The biosorption equilibrium data fitted well to the Langmuir isotherm. Coated

Sesham Sawdust (dalbergia sissoo) shown the highest adsorption capacity for hexavalent chromium

ions. Sesham Sawdust is easily avialable plant waste and can, therefore, be used in batched reactors in

small scale industries having Cr (VI) in waste water.

Acknowledgement:- The authors are thankful to University Grants Commission, New Delhi for

providing financial assistance and fellowship to SCS for this project.

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Documents

Lalit Sharma *, 2 · 1 Lalit Sharma *, 2 Subhash Chander Sharma Address For correspondence: 1, 2 PTU Regional Centre for PG studies (Environmental Science & Engineering), Shaheed

Lalit Sharma , 2 · 1 Lalit Sharma , 2 Subhash Chander Sharma Address For correspondence: 1, 2 PTU Regional Centre for PG studies (Environmental Science & Engineering), Shaheed