Kinetic modeling: Chromium(III) removal from aqueous ... - NOPR

Journal of Scientific & Industrial Research

640 Vol. 68, July 2009, pp. 640-646

J SCI IND RES VOL 68 JULY 2009

Kinetic modeling: Chromium(III) removal from aqueous solution by microbial waste biomass Indu Sharma and Dinesh Goyal* Department of Biotechnology and Environmental Science, Thapar University, Patiala 147 004, India Received 05 September 2008; revised 27 March 2009; accepted 02 April 2009 This study presents removal of chromium (III) from aqueous solution by microbial waste biomass (MB2) obtained as a byproduct of pharmaceutical fermentation industry. Sorption kinetic behavior of Cr(III) was studied in a series of experiments in batch mode at different pH, adsorbent dosage and initial Cr concentration. Optimum Cr(III) removal (73.9%) from aqueous solution was at pH 4 by 1% biomass dosage. A comparison of kinetic models (Lagergren, Ho & McKay, Elovich & MorrisWeber) and correlation coefficient (R2) indicated that Ho & McKay kinetic model correlates well with experimental kinetic data. Keywords: Aqueous solution, Chromium (III), Kinetic modeling, Microbial waste biomass, Streptomyces sp., Tannery effluent

Introduction Trivalent chromium [Cr(III)], widely used in industries (steel production, leather tanning, paints and pigments, metal plating) and other applications, is responsible for environmental pollution1,2. Cr(III) is relatively insoluble in water and less toxic than hexavalent chromium3. Conventional methods (precipitation, oxidation/ reduction, ion exchange, filtration, membranes and evaporation) are extremely expensive or inefficient for metal removal and create sludge disposal problems4-6. Biosorption from industrial or natural sources may provide an efficient and competitive solution to treat wastewater. Biosorbents are prepared from bacteria, fungi and algae including waste biomass of fermentation and pharmaceutical industries7-8. In this study, microbial waste biomass (MB2) from fermentation industry was used for Cr (III) removal from aqueous solution. Kinetics was studied at varying pH, adsorbent dosage and initial Cr(III) concentrations. Materials and Methods Microbial waste biomass of Streptomyces sp. (MB2) was obtained as a waste byproduct of pharmaceutical fermentation industry in fermentative production of antibiotics. Biomass collected from Ranbaxy (fermentation industry) Paonta Sahib, HP, India was grinded in a blender, sieved (size, 2.0 mm) and washed *Author for correspondence E-mail: [email protected]

with distilled water before drying at 80°C for overnight or till moisture reduced to below 5%. Physico-chemical analysis of biomass was done as per reported9 method. Tannery effluent was collected from AV Tanneries, Kapurthala, Punjab, India and characterized10-11. Preparation of Aqueous Solution

Aqueous solution of chromium was prepared by dissolving required quantity of Cr2O12S3 in distilled water. Stock solution and tannery effluent were diluted with distilled water to obtain working solution (5- 50 mg/l) for further experiments. Desired pH of solution was adjusted with 1N NaOH and 1N HCl. Batch Kinetic Study

Batch experiments were conducted with MB2 in Erlenmeyer flask (250 ml) using different biomass dosage (0.25-2%) and aqueous solution (100 ml) of Cr(III) (25 mg/l). Suspension was shaken at 120 rpm, 28°C for 24 h. Similarly, experiments were conducted at different pH (2-5) and Cr(III) concentration (5-50 mg/l). Residual concentration of Cr(III) in aqueous solution was measured by atomic absorption spectrophotometer (AAS) with an air-acetylene flame using Cr-hallow cathode lamp having sensitivity limit of 0.05 ¼g/ml. Working standard solution of Cr(III) was prepared from stock (1000 mg/l) procured from Acros Organic Ltd, New Jersey, USA. Triplicates of each sample were analyzed. Mean value and relative standard deviation as given by AAS were recorded. Cr(III) uptake (qe) by biomass was calculated as

SHARMA & GOYAL: CR(III) REMOVAL FROM MICROBIAL WASTE BIOMASS

qe =

(C i − C f )V

…(1)

m

where, Ci and Cf , initial and final Cr(III) concentrations, mg/l; V, Cr(III) solution volume, ml; m, biomass wt, g. Removed Cr(III) ions (R%) was calculated as

R(%) =

(C i − C f ) Ci

Χ100

…(2)

Results and Discussion Physico-chemical parameters of MB2 are as follows: pH, 6.50±0.43; bulk density, 0.70±0.21 g cm3; ash, 5.70±0.60%; moisture, 5.00±0.40%; carbon, 45.77±1.20%; hydrogen, 6.79±0.22%; nitrogen, 8.53±0.34%; and calorific value (CV), 17.25±1.30 MJ/ kg. CV (17.25 MJ/kg) of MB2 (Streptomyces sp.) coincides with relative CV (17.5 MJ/kg) of biomass solid fuels, municipal waste, industrial waste, peat and brown coal9. Greenish tannery effluent [pH, 3.5; Cr(III), 1700.9 mg/l; total solids, 96,000 mg/l; total dissolved solids, 80,000 mg/l] had chemical oxygen demand (COD) of 332.8 mg/ l and biochemical oxygen demand (BOD) of 290 mg/l. Traces of other metals (Fe, Pb Co, Cu, Cd), and secondary elements (Ca, Mg and Na) were also present. Batch Kinetic Study

Batch sorption studies on Cr(III) removal from aqueous solution by MB2 was carried out to optimize adsorbent dosage, pH, contact time, Cr(III) concentration and removal of Cr(III) from tannery effluent. Effect of Adsorbent Dosage

Effect of adsorbent dosage (0.25-2%) on sorption of Cr(III) from aqueous solution (pH 4) containing Cr(III) (25 mg/l) with agitation rate of 120 rpm at ambient temperature was studied. Increasing adsorbent dosage (0.25-2%), Cr(III) removal increased (45.84-54.89%) by MB2 (Streptomyces sp.). Similar observations were made with Aspergillus sp 12 and Streptomyces noursei13, which showed 70-75% removal of Cr(III) from aqueous solution and exhibited an adsorption capacity14 (1.8-2.0 mg/g) comparable with MB2 (2.24 mg/g) and commercial activated carbon1 (2.7 mg/g). Effect of pH

Amount of Cr(III) adsorbed increased from 0.27 to 1.21 mg/g (72.38%) by MB2 as pH increased from 2 to

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515-16. Beyond pH 6.0, experiment was not done due to possibility of Cr(III) precipitation17. Maximum Cr(III) removal was achieved between pH 4-6, at which biomass surface is negatively charged1,2. Adsorption of Cr(III) is therefore an electrostatic interaction between biomass and Cr(III) cations. Ramos et al18 reported that Cr(III) is not adsorbed at pH below 2 and Cr(III) is precipitated at pH above 6.4. Effect of Chromium Concentration

Kinetics of Cr(III) removal by MB2 was studied at varying initial concentrations (5-50 mg/l) of Cr(III) in aqueous solution as well as from tannery effluent. Maximum Cr(III) removal capacities of MB2 from aqueous solution and tannery effluent were 24.9-68.2 % and 41.2-73.9%, respectively in batch mode. Equilibrium uptake of Cr(III) increased in aqueous solution (0.08-2.89 mg/g) and tannery effluent (0.17-4.5 mg/g). Earlier reports16 also indicated that removal of Cr(III) was dependent on Cr(III) concentration because increase in initial Cr(III) concentration (50-300 mg/l) increased adsorbed amount of Cr(III). Effect of Contact Time

With increase in contact time (0.08-4 h), Cr(III) removal increased from aqueous solution (40-70%) and tannery effluent (11.5-57%) by MB2. Maximum Cr(III) removal from aqueous solution (65%) and tannery effluent (57.34%) was observed within first 2 h. Lower removal rate in latter stage was due to difficulty faced by Cr ions to occupy remaining vacant surface sites because of forces between solute molecules of solid and liquid phase19. Therefore, adsorption is rapid and ultimate adsorption (40-45%) occurs within first hour of contact and saturation is reached within next 48 h1,8. Diminishing removal with increasing time may also be due to intraparticle diffusion process dominating over adsorption20. Kinetic Modeling

Number of models have been developed to describe kinetics of metal biosorption in batch experiment1,2. Kinetic modelling of Cr(III) describes solute uptake rate, which controls residence time of adsorbate uptake at solid-solution interface. Conformity between experimental data and models predicted values was expressed by correlation coefficients (R2, values close or equal to 1). A relatively high R 2 value indicates that model successfully described kinetics of Cr(III) adsorption.

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Table 1—Adsorption kinetic models for Cr(III) removal by microbial waste biomass (MB2) at different pH (Ci =50 mg/l, adsorbent dosage 1%, pH 4, 120 rpm) pH

Lagergren equation R2

Ho & McKay equation R2

Elovich equation R2

Morris-Weber equation R2

2.0 3.0 4.0 5.0

0.23 0.71 0.94 0.78

0.99 0.84 0.99 0.99

0.02 0.55 0.96 0.95

0.13 0.47 0.97 0.85

Table 2—Adsorption kinetic models for Cr(III) removal by microbial waste biomass (MB2) at different biomass dosage (Ci =50 mg/l, pH 4, 120 rpm) Biomass dosage 0.25 0.5 1.0 2.0



Elovich equation R2


0.58 0.71 0.46 0.44

1.00 0.99 0.99 1.00

0.93 0.94 0.83 0.81

0.74 0.85 0.80 0.60

Table 3—Adsorption kinetic models for Cr(III) removal by microbial waste biomass (MB2) at different concentration (Adsorbent dosage 1%, pH 4, 120 rpm) Chromium conc, mg/l 5 10 20 50



Elovich equation R2


0.51 0.57 0.71 0.90

0.99 0.99 0.99 0.99

0.86 0.83 0.93 0.99

0.69 0.56 0.79 0.83

Non-linear regression analysis was applied to each set of data. A correlation coefficient (R2) and a probability value (p) represent “goodness of fit” for models to the data obtained by linear as well non-linear regression. Lagergren Equation (Pseudo-First-Order)

applying initial conditions (t = 0 to t = t and qt = 0 to qt = qt), integrated form of Eq. (3) becomes

log(q e − qt ) = log( qe ) −

kl t 2.303

…(4)

Sorption kinetic model21 is expressed as

dqt = kl (qe − qt ) dt

…(3)

where qe and qt (mg/g), adsorption capacity at equilibrium and at time t, respectively; kl, rate constant of pseudo first-order adsorption process. After integration and

Plot of log (qe-qt) vs t should give a linear relation, from which kl and qe can be determined from slope and intercept of plot, respectively. R2 of Cr(III) under different conditions were calculated from plots at different pH (Table 1), biomass dosage (Table 2) and Cr(III) concentration (Table 3). In most of the cases, first-order equation of Lagergren did not apply throughout the contact time and is generally applicable over initial (20-


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0.6

log (qe-q t )

0.5

y = -0.0315x + 0.4375 R2 = 0.8988

0.4 0.3 0.2 0.1 0.0 0

2

4

6

8

10

12

Time, hh) Fig. 1—Lagergren plot of Cr(III) onto microbial waste biomass (MB2) Ci= 50mg/l

30 min) sorption1,21. A plot of log (qe-qt) versus agitation time, gave a straight line with R2 of 0.94 for MB2 at pH 4 (Tables 1-3). Results showed that adsorption reaction can be approximated with pseudo first-order kinetic model. It was observed that k1 (0.03-0.88) and qe (1.422.74) increased at different adsorbent dosage (0.25-2%). Values of k1 (0.84-0.05) and qe (1.83-0.95) decreased at different pH. In most of the cases, first-order equation of Lagergren did not apply throughout complete range of contact time and is generally applicable over initial (20-30 min) sorption process. Plots of log (qe-qt) vs time (t) (Fig. 1) deviated considerably from theoretical data after a short period. Slope and intercepts as calculated from plots were used to determine k1 (first-order rate constant) and equilibrium capacity (qe). Values of qe are found lower than experimental one. Therefore, chromium-adsorbent systems do not follow a first-order rate equation1,22,23. Ho and McKay Equation (Pseudo-Second-Order)

Sorption kinetic model by Ho & McKay24,25 equation and adsorption kinetics rate is expressed as

dqt = k 2 ( qe − qt ) 2 dt

…(5)

where k2 is rate constant of Ho & McKay equation (g/ mg/min). For boundary condition (t = 0 to t =t and qt = 0 to qt =qt), integrated form of Eq. (5) becomes

l l = + kt (qe − qt ) qe

…(6)

This is integrated rate law for a pseudo second-order reaction. Eq. (6) can be rearranged as

t   qt

 l l  = + (t ) 2 qe  k 2 qe

…(7)

If initial adsorption rate, h (mg/g/min) is h = k 2 qe , then Eq. (7) becomes 2

 t   qt

 l l  = + (t )  h qe

…(8)

Plot of (t/qt) and t of Eq. (7) should give a linear relationship, from which qe and k2 can be determined from slop and intercept of plots, respectively (Fig. 2). R2 for linear plots are found superior (in most cases e”0.99) (Tables 1-3). It was observed that k2 (0.99-0.97) and h (6.32-25.38) increase with increase in biomass dosage. Values of k2 (0.29-2.94) and h (0.90-5.20) increased with increase in initial Cr(III) ions. Values of h and k2 were found higher for MB2 at different parameters [dosage, pH and Cr(III) concentration]. Experimental points shown together with theoretically generated values reflect extremely high correlation coefficients (Table 1-3). Data showed good compliance with pseudo-second order kinetic model1,16,17 (R2 > 0.99). However, these two models do not provide a definite mechanism. Therefore, another simplified model24,25 was tested, in which kinetic data is better fitted by second-order rate equation1,22,23

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9.0

t/qt

8.0 7.0 6.0 5.0 4.0 3.0

y = 0.3401x + 0.1925 R2 = 0.9985

2.0 1.0 0.0 0

5

10

15 Time, h

20

25

30

h)

Fig. 2—Ho & Mckay equation for Cr(III) onto microbial waste biomass (MB2) Ci= 50 mg/l

3.5 3.0 2.5

qt

2.0 1.5 y = 0.3507x + 1.8957 R2 = 0.9859

1.0 0.5 0.0 -3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

ln(t) Fig. 3—Elovich equation for Cr(III) onto microbial waste biomass (MB2) Ci= 50 mg/l

4.0 3.5

-1

qt (mg.g )

3.0 2.5 2.0 1.5

y = 0.4031x + 1.3595 R2 = 0.8309

1.0 0.5 0.0 0

1

2

3

4

5

6

Time,h) h Fig. 4—Morris-Weber equation for Cr(III) onto microbial waste biomass (MB2) Ci= 50 mg/l


(Fig. 2). Experimental qe values were compared with qe value determined by pseudo-first and second-order rate kinetic models, which suggests that sorption system is not a pseudo first-order reaction and that a pseudosecond-order model can be considered23. Elovich Equation

Elovich model equation is generally expressed as26

dqt = α exp(− β qt ) dt

…(9)

where, α initial adsorption rate (mg/g/min); β, desorption constant (g/mg) during any one experiment. To simplify Elovich equation, Chien & Clayton assumed αβt >> t and by applying boundary conditions (qt = 0 at t = 0 and qt =qt at t = t), Eq. (9) becomes

qt =

l ln (αβ ) + ln (t ) β

…(10)

If Cr(III) adsorption fits Elovich model, a plot of qt vs ln (t) should yield a liner relationship with a slope of (l/β) and an intercept of (1/ β) ln (± β) (Fig. 3). R2 were determined from plot between qt and ln (t), respectively at different pH, biomass dosage and chromium concentration (Tables 1-3). Computed value of α and β were calculated at biomass dosage [α (18.18-0.26), β (9.42-34.13)], pH [α(-3.69-94.32) β (-29.71-9.45)] and Cr(III) concentration [α (7.55-78.07) β (26.25-2.85)]. Sorption kinetics of Cr(III) examined using Elovich model gave R2 of 0.96 for MB2, which indicates that dynamics data fitted for biomass at pH 4.

adsorption mechanism, which is related to an improved bonding between Cr(III) ions and adsorbent particles. Conclusions Microbial waste biomass comprising of Streptomyces sp. involved in fermentation process was effective in removal of Cr(III) from aqueous solution as well as tannery effluent. Maximum chromium removal capacities of Streptomyces sp. biomass (MB2) were 24.9-68.2 % from aqueous solution and 41.2-73.9% from tannery effluent at ambient temperature, rpm 120, and initial concentration (50 mg/l) of Cr(III). A comparison of kinetic models (Lagergren, Ho & McKay, Elovich & MorrisWeber) applied to MB2 indicates that adsorption of Cr(III) on MB2 follows a best Ho & McKay pseudo second-order rate equation and correlation coefficient (R2) correlated with experimental data. Removal of Cr(III) from aqueous solution was possible using MB2 from pharmaceutical fermentation industry. MB2 offers an alternative adsorbent for removal of Cr(III) from wastewater such as tannery effluent. This can provide means for using solid waste of one industry to treat chromium containing effluents from another industry for development of a suitable cost effective biosorbent. Acknowledgement Authors thank CSIR, New Delhi, for providing financial support, Ranbaxy Paonta Sahib, H P, India for providing microbial biomass and Director, Thapar University for providing infrastructural support. References

Morris-Weber Equation

Intraparticle diffusion model of Cr(III) is expressed as by Weber & Morris27 and Srivastava et al28. Sorption kinetics of Cr(III) was also examined by using MorisWeber equation as

qt = Rid t

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1

2

…(11)

where, qt,, sorbed concentration at time t; Rid , rate constant of intraparticle transport. qt was plotted against t1/2 (Fig. 4). Sorption follows linearity as per Eq (11) with R2 (0.831). Value of Rid was computed from slope of plot. Value of R2 was (Table 1-3): pH, 0.13-0.85; biomass dosage, 0.74-0.59; and Cr(III) concentration, 0.69-0.83. Values of Rid were calculated from slope of such plots (Fig. 4) and R 2 values led to the conclusion that intraparticle diffusion process is rate-limiting step. Higher values of Rid illustrate an enhancement in the rate of adsorption, whereas larger Rid values illustrate a better

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