Optimization of Lead Adsorption Using Animal Bio Polymers by Factorial Design

A. Ratna Kumari et al., IJSID 2011, 1 (3), 303-319

International Journal of Science Innovations and Discoveries, Vol ume 1, Issue 3, November-December 2011

303

OPTIMIZATION OF LEAD ADSORPTION USING ANIMAL BIOPOLYMERS BY FACTORIAL DESIGN

A. Ratna Kumari1*, U.Kiran Babu2, K. Sobha3

1Department of Biotechnology, Bapatla Engineering College (autonomous), Bapatla-522 101, AP, India & Centre for

Biotechnology, Acharya Nagarjuna University, Nagarjuna Nagar, Guntur-522 510, A.P., India, 2Department of

Biotechnology, Bapatla Engineering College, Bapatla-522 101, AP, India, 3Department of Biotechnology, RVR & JC

College of Engineering, Chowdavaram, Guntur – 522 019, AP, India.

INTRODUCTION

ISSN:2249-5347 IJSID

International Journal of Science Innovations and Discoveries An International peer

Review Journal for Science

Research Article Available online through www.ijsidonline.info

Received: 14.09.2011

Modified: 16.10.2011

Published: 29.12.2011

Key words: Adsorption,

Animal biopolymers,

Factorial design, lead.

*Corresponding Author

Address:

Name:

A. Ratna Kumari

Place:

Guntur, AP, India

E-mail:

[email protected]

ABSTRACT

Heavy metals present in the industrial effluents remain as alarming

pollutants due to their nondestructive nature, toxicity, bioaccumulation and

subsequent biomagnification. Animal biopolymers viz., chick and duck feathers’

fibers were treated with 5% tannic acid solution. From the preliminary studies it

was found that pH, contact time, and biosorbent dose are significant factors for

maximal biosorption of lead by both chick and duck feathers. To study the

interactive effects of these three independent parameters (Biosorbent dosage,

Contact time, pH) and their optimization for lead biosorption process by response

surface methodology (RSM), Box-Behnken design (BBD) was applied. The

regression equation coefficients (r2) are 0. 98098 & 0.91785 for chick and duck

feathers respectively and the data fitted to a second-order polynomial equation for

removal of lead (Pb). The critical values of the three parameters obtained for chick

feathers, with a maximum biosorption efficiency of 70.73%, are 1.9 g/L of

biosorbent, 24.56 hours of contact time, 6.94 pH. For duck feathers with a

maximum biosorption efficiency of 58.8%, the critical values obtained are 2.3 g/L

of biosorbent, 20.17 hours of contact time and 7.02 pH.



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INTRODUCTION

Water bodies are being overwhelmed with bacteria, waste matter and toxic substances (1). Among toxic

substances reaching hazardous levels are heavy metals (2). Contamination of water supplies with heavy metals is an

area of concern both nationally & internationally where the challenge to remediate hazardous metal containing

waste streams from present or past mining operations, industrial sites and ground waters is immense (3). Heavy

metals of concern include lead, chromium, mercury, uranium, selenium, zinc, arsenic, cadmium, silver, gold and

nickel (4). Heavy metal pollution in the aquatic system has become a serious threat today as they are non-

biodegradable and thus persistent (5). Metals are mobilized and carried into food web as a result of leaching from

waste dumps, polluted soils and water. The metals increase in concentration at every level of food chain and are

passed onto the next higher level–a phenomenon called bio-magnification (6) and cause several diseases and health

disorders in humans, and other living organisms (7). Thus, removal of heavy metals from industrial wastewater is of

prime importance (8).

Some of the conventional techniques for removal of metals from industrial wastewater include adsorption

(9), sedimentation (10), electrochemical processes (11), ion exchange (12), biological operations (13), cementation (14) ,

coagulation / flocculation (10) , filtration and membrane processes (14) , chemical precipitation and solvent

extraction (15- 16) . However, most available methods may show economical and technical disadvantages such as

high capital and operational costs, high sensitivity to operational conditions, significant energy consumption, or

sludge generation (17) & they also are ineffective when metals are present in high concentrations in aqueous

solution (18). With increasing environmental awareness and stringent government policies, it has become necessary

to develop new environmental friendly ways to clean up contaminants using low-cost methods and materials (19).

In this aspect, the relatively new technology termed biosorption has dominated. The major advantages of

biosorption over conventional treatment methods include low cost, the use of inexpensive and never exhausted

biosorbent materials, high efficiency of metal removal from dilute solutions, minimization of chemical and/or

biological sludge, no additional nutrient requirement, regeneration of biosorbent and the possibility of metal

recovery (20). The biosorption process involves a solid phase (sorbent or biosorbent; usually a biological material)

and a liquid phase (solvent, normally water) containing a dissolved species to be sorbed (sorbate, a metal ion) (1).

An adsorbent material (biosorbent), both living and nonliving, derived from suitable biomass can be used for the

effective removal and recovery of heavy metal ions from wastewater streams (21-22). Recently, the use of non-living

biomaterials as metal-binding compounds has been gaining advantage as these compounds require minimum care

and maintenance and can be obtained more cheaply (23) . Biomaterials of animal origin, generated as waste such as

animal bones (24-25), chick feathers (26) and duck feathers (27) have been used for removal of heavy metals.

In particular, lead has been classified as a serious hazardous heavy metal with high priority in the context

of environmental risk (17). This metal is extremely toxic and can damage kidney, liver, brain and reproductive

organs besides other adverse effects to humans (7) . At present, lead pollution is considered a worldwide problem



305

because this metal is commonly detected in several industrial wastewaters (28). Examples of these wastewaters are

those produced by processes such as mining, smelting, printing, metal plating, explosive manufacture, and dying.

Electroplating mainly discharges huge amounts of lead and its ingestion beyond the permissible level causes

various types of acute disorders in man such as anemia, alimentary symptoms, wrist and foot drop, renal damage,

embryo toxicity resulting in spontaneous abortions and sometimes encephalopathy. In children it causes

behavioral effects and intellectual impairment. In this context, local legislations have established rigorous

standards for lead concentrations in industrial effluents. Therefore, special attention has been given to develop

proper methods for lead removal from water (29).

During the last decade, several studies have shown that different synthetic and natural sorbents can be

used to remove lead ions from aqueous effluents (30-48). Many examples of natural sorbents are available in the

literature, and they include brewery biomass, cactus pulp, olive stone waste, chitosan, modified wool, cotton,

nutshells, rice hulls, pine bark, sawdust, sugar cane bagasse, fruit stones, and pyrolyzed coffee, among others (41-48).

In removal processes, most of these sorbents generally show Pb uptakes in the range of 1.0 - 100 mg/g. In

particular, chicken feathers and duck feathers are among the natural sorbents that can be used for water treatment

(27, 49-54). The feathers represent four to six percent of the total body weight and, as a consequence, are a waste

product generated in large quantities from commercial poultry industry. As a natural protein material, feather

fiber has polar and ionizable groups on the side chain of constant amino acid residues, which are able to bind

charged species. The adsorption of metal cations to feather fibers can be attributed to many characteristics such as

low solubility, complex physical form, relatively high content of reactive groups that can serve as binding sites or

that can be chemically modified, variety and juxtaposition of reactive sites that can allow cooperative reaction etc.

To date, the use of chicken feathers for sorption purposes has achieved satisfactory results for the removal of some

heavy metals, colorants, and organic toxic compounds (39, 49-54) & duck feathers are also used for the removal of

heavy metals (27).

Biosorption efficiency depends upon many factors, the critical ones being pH, contact time, and biosorbent

concentration. This work is, therefore, primarily aimed at evaluating the effects of pH, contact time, and biosorbent

dose on the percentage removal of lead by both Chick and Duck feathers. To study the cumulative/interactive effect

and optimization of lead biosorption process, a Factorial design was applied, varying the three independent

parameters (initial pH, Contact time, Biosorbent dosage). Response surface methodology was applied to the Box

and Behnken experimental design(55). To the best of our knowledge, there is no published report on optimization of

biosorption process for removal of lead with animal biopolymers (Chick and Duck feather) using response surface

methodology. As the Box–Behnken design minimizes the number of factor combinations and maintains good

precision of the predicted response (56-58), this matrix has been used for the optimization of biosorption process for

removal of lead using animal biopolymers (Chick and Duck feathers).



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MATERIALS AND METHODS

Biosorbent preparation

Chick and Duck feathers were collected from poultry processing facilities. The feather fibers used were in

the form of barbs which were detached from the shaft of Chicken feathers and Duck feathers. These were washed

several times with deionised water. Feather fibers were immersed in 5% (w/v) aqueous solution of the Tannic acid

(material-to-liquor ratio 1:100) at 70°C for 1–13 hr. Tannic acid (TA) is a kind of plant polyphenol. It is reported

that TA can form insoluble products with keratin by tanning reaction, which can increase the chemical and physical

stability of protein. Moreover, TA can form chelates with many metal cations via the ortho dihydroxy (catehol) or

trihydroxy-benzene (galloyl) group (59). Feather fibers were removed after the incubation time, washed thoroughly

in a porcelain funnel with distilled water, and then dried at room temperature before metal adsorption

experiments.

Preparation of metal solution

All the reagents were Analytical Reagent Grade and were prepared in Double Distilled water. Dissolved

1.5980g of lead nitrate (Pb (NO3)2 ) in 100ml of Double Distilled water, diluted to 1 liter in a volumetric flask with

Double Distilled water. This was used as the source of Pb in the synthetic waste water. pH of the solution was

adjusted using 0.1N HCl or NaOH. Solutions of varying concentrations were prepared by diluting the stock solution

with Double Distilled water. Fresh dilutions were used for each adsorption study.

Lead (Pb) ion determination

The change in Pb concentration due to adsorption was determined using AAS (Atomic absorption

spectrophotometer) in flame at a wavelength of 283nm.

Effect of biosorbent concentration on Adsorption

The adsorption of lead by Chick and duck feather fibers was studied at increasing concentration of

biosorbent 0.05g, 0.10g, 0.15g, 0.20g, 0.25g, 0.30g respectively in 100ml of lead solution in 250 ml Erlenmeyer

flask at constant incubation time and pH 7. Final values were projected in g/L. The biosorbent was removed from

the solution by centrifugation and the supernatant was analyzed for the residual concentrations of lead ion using

Atomic Absorption Spectrophotometer. Each adsorption experiment was carried out twice, and the average was

used for adsorption study.

Effect of Contact Time on Adsorption

Optimum biosorbent concentration obtained for chick and duck feather were taken to monitor the effect of

time on adsorption. The adsorption experiments were carried out at different contact times viz., 5, 10, 15, 20, 25,

35, 45, 55, 65min with a fixed adsorbent dose at pH 7. The biosorbent was removed from the solution by

centrifugation and the supernatant was analyzed for the residual concentrations of lead ion using Atomic

Absorption Spectrophotometer.



307

Effect of pH on Adsorption

Optimum Biosorbent concentration and optimum contact time were used to monitor the pH effect on

adsorption. The adsorption experiments were carried out for different pH values 4-9 with a fixed adsorbent dose

concentration at optimum contact time. The biosorbent was removed from the solution by centrifugation and the

supernatant was analyzed for the residual concentrations of lead ion using Atomic Absorption Spectrophotometer.

Factorial Design

The Box–Behnken design (BBD) model, which is the standard RSM, was established using STATISTICA 6.0

for the optimization of biosorption process. The experimental design, three independent variables, i.e. pH (6.0-8.0),

time (15-35hrs) and biosorbent concentration (0.1-0.3g/100ml) were taken to effect biosorption of lead ions. The

experimental design was applied after selection range of each variable (maximum and minimum) as shown in

Table 1. The Box–Behnken design contained a total of 27 experiments. All the biosorption experiments were

conducted in 250mL Erlenmeyer flasks and then the filtrate was analyzed for residual lead concentration using

Atomic absorption spectrophotometer.

Statistical analysis

The quadratic equation model for predicting the optimal point was expressed according to the following

equation:

Y= β0 + Σ βi Xi + Σ βii Xi2 + Σ βij Xi Xj

where Y is the predicted response, β0 model constant; βi is linear coefficient, βii is the quadratic coefficient

and βij is the different interaction coefficients of the model;

In this study, the removal of lead was processed using the following equation

Y= β0 + Σ βi Xi + Σ βij Xi2 + Σ βij Xi Xj

= A0 + A1x1+ A2x2 + A3x3 + A4x1x2+ A5x1x3 + A6x2x3 + A7x1x1 + A8x2x2 + A9x3x3

in which Y is the response variable, percentage removal of lead and X1, X2 and X3 are the coded values of the

independent variables- biosorbent concentration, time, pH respectively.

STATISTICA 6.0, was used for regression analysis of the data obtained and to estimate the coefficient of the

regression equation. The quality-of-fit of polynomial model was expressed by the coefficient of determination r2

and statistical significance was checked. To visualize the relationship between responses and experimental levels

for each of the factors, the fitted polynomial equation was expressed as surface plots. Three dimensional plots

demonstrate relationships between the lead ion uptake with the paired factors (when other factor was kept at its

optimal level), describing the behavior of biosorption system in a batch process.



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Table 1: Box–Behnken design for the optimization of Biosorption of Lead (Pb) using Chick Feather

RESULTS & DISCUSSION

On treatment with tannic acid the chick & duck feather protein chemical and physical stability was

increased. 1ppm, 2ppm, 3ppm, 4ppm, and 5ppm lead solutions were prepared using stock solution. Absorbance

values were taken using atomic absorption spectrophotometer. Standard graph was plotted by taking known

concentration on X-axis and absorbance at 283 nm on Y-axis which is shown in Fig-1 and it obeyed Beer-lambert’s

law.

Effect of biosorbent concentration

Lead biosorption by chick & duck feathers were studied at various biosorbent concentrations ranging from

0.05g to 0.3 g in 100ml of 5ppm lead solution. The percent removal of lead increased with an increase in

biosorbent concentration because of an increasing adsorption surface area. The maximum biosorption efficiency

was obtained at 0.2 g of chick feather and 0.15g of duck feather, but further increase in biosorbent concentration

Box–Behnken design Chick feathers Duck feathers

Run

No

Biosorbent

Concentration

(g/100ml)

Time

(hrs)

pH % Removal

Efficiency

(Observed)

% Removal

Efficiency

(Predicted)

% Removal

Efficiency

(Observed)

% Removal

Efficiency

(Predicted)

1 0.1 15 6 41.46 39.2797 35.7 33.4519

2 0.1 15 7 43.90 43.3036 37.8 36.0796

3 0.1 15 8 46.34 45.7142 38.1 37.7963

4 0.1 25 6 48.78 50.6497 39.0 39.4657

5 0.1 25 7 53.65 53.6811 41.4 41.5852

6 0.1 25 8 53.69 55.0992 42.7 42.7935

7 0.1 35 6 56.09 55.7664 43.8 45.3685

8 0.1 35 7 57.33 57.8053 45.8 46.9796

9 0.1 35 8 58.29 58.2308 46.9 47.6796

10 0.2 15 6 60.48 64.4042 47.7 50.4657

11 0.2 15 7 63.41 65.8322 48.6 51.6519

12 0.2 15 8 65.85 65.6469 50.1 51.9269

13 0.2 25 6 68.29 67.4400 51.5 52.3296

14 0.2 25 7 70.73 67.8756 52.2 53.0074

15 0.2 25 8 68.29 66.6978 54.1 52.7741

16 0.2 35 6 65.85 64.2225 56.5 54.0824

17 0.2 35 7 63.41 63.6656 58.9 54.2519

18 0.2 35 8 60.97 61.4953 54.4 53.5102

19 0.3 15 6 56.09 53.6319 52.8 51.0352

20 0.3 15 7 53.65 52.4642 51.1 50.7796

21 0.3 15 8 48.78 49.6831 50.9 49.6130

22 0.3 25 6 47.07 48.3336 49.0 48.7491

23 0.3 25 7 46.34 46.1733 48.1 47.9852

24 0.3 25 8 41.51 42.3997 47.0 46.3102

25 0.3 35 6 36.40 36.7819 45.3 46.3519

26 0.3 35 7 32.01 33.6292 43.5 45.0796

27 0.3 35 8 30.11 28.8631 41.1 42.8963



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decreased the maximum removal of metal ions because of saturation of biosorbent surfaces as shown in Fig- 2. The

percentages of removal of lead by chick and duck feathers were 41.6% and 37.5% respectively.

Fig- 1 Standard graph of lead

0

5

10

15

20

25

30

35

40

45

0.05 0.1 0.15 0.2 0.25 0.3

% r

em

ov

al

biosorbent concentration(g/100ml)

% removal by C.F.

% removal by D.F.

Fig - 2 Effect of biosorbent concentration (give units correctly) on biosorption using chick feather (C.F.) and duck

feather (D.F.)

Effect of contact time

The contact time was evaluated as one of the important parameters affecting the biosorption efficiency.

The adsorption experiments were carried out for different contact times with a fixed adsorbent dose concentration

at pH 7. Fig - 3 shows the biosorption efficiency of lead ions by chick and duck feathers as a function of contact

time. The lead uptake was found to increase with increase in contact time up to 25hrs for chick feathers & 35hrs

for duck feathers and after that, lead uptake slowly decreased. The fast initial metal biosorption rate was attributed

to the surface binding and the following slower sorption was attributed to the interior penetration (60). Different

kinds of functional groups, with different affinities to the metal ions, are usually present on the surface of feathers.



310

The active binding groups with higher affinities are firstly occupied (61). The percentages of removal of lead by

chick and duck feathers were 69.3% and 55.83% respectively.

Effect of pH

Biosorption of heavy metal ions is dependent on the pH of solution as it affects biosorbent surface charge,

degree of ionization etc. The pH of the solution influences both metal binding sites on the feather surface and the

chemistry of metal in solution. In order to demonstrate the effect of pH on biosorption capacity, uptake of lead ions

onto chick and duck feathers as a function of pH was studied in the pH ranges of 4 to 8 with a fixed adsorbent dose

concentration at optimum contact time. The percentages of removal of lead by chick and duck feathers

were76.66% and 58.95% respectively at pH7 as shown in Fig-4.

0

10

20

30

40

50

60

70

80

5 10 15 20 25 35 45 55 65

% r

em

ov

al

Time(hours)

% removal by C.F.

% removal by D.F.

Fig - 3 Effect of time on biosorption using chick feather (C.F.) and duck feather (D.F.)

0

10

20

30

40

50

60

70

80

90

4 5 6 7 8

% r

em

ov

al

pH

% removal by C.F

% removal by D.F

Fig-4 Effect of pH on biosorption using chick feather (C.F.) and duck feather (D.F.)



311

Factorial Design

The independent variables like biosorbent concentration, time, pH were used to optimize the adsorption by

chick and duck feathers and the results of percentage removal of lead in each case are presented in Table 1. The

percentage removal of lead depends on the individual effects of combinations of independent variables and the

results show a significant variation for each combination. Multiple regression analysis of the experimental data

was obtained from the following regression equation for the biosorption of lead

Equation-1

Y= β0 + Σ βi Xi + Σ βij Xi2 + Σ βij Xi Xj

= A0 + A1x1+ A2x2 + A3x3 + A4x1x2+ A5x1x3 + A6x2x3 + A7x1x1 + A8x2x2 + A9x3x3

The coefficients (p) were highly significant for both chick and duck feathers when compared with interactive

effects. Multiple regression coefficient (R) was estimated from the second-degree polynomial Eq. (1). The value of

r2 = 0. 98098 & 0.91785 for chick and duck feathers respectively which is closer to one indicates that the

correlation is best suited for predicting the performance of the biosorption system and the predicted values were

found to be very closer to the experimental results. The results obtained from the BBD, the student’s ‘T’

distribution, the p values and the parameter estimates for chick and duck feathers are given in Table 2& 3

respectively. The regression equation coefficients were calculated and the data fitted to a second-order polynomial

equation using MATLAB for removal of lead with chick & duck feathers. The optimum values of the test variables

and the corresponding maximum percentage removal of lead (70.73%) by chick feathers were obtained in coded

units as X1 =1.0705, X2 = 0.0038, X3 = 0.0186 & maximum percentage removal of lead (58.8%) by duck feathers

were obtained in coded units as X1 =565.5556, X2 = 1.3436, X3 = 10.7542 were shown in the following equations.

Final Polynomial Equation for chick feathers:

Y= -0.1456 + 1.0705x1 + 0.0038 x2+ 0.0186 x3 -0.0083x1x2-0.0260 x1x3 - 0.0001 x2x3- 1.7948 x1x1 -0.000

x2x3 - 0.0008 x3x3

Final Polynomial Equation for duck feathers:

Y= -63.5856+ 565.5556x1 + 1.3436 x2 + 10.7542 x3 -4.1500 x1 x2 -14.4167 x1 x3 -0.0508 x2x3 -822.2222

x1 x1 – 0.0006 x2 x3 - 0.4556 x3 x3

The maximum lead removal by chick and duck feathers was 70.73% and 58.8 respectively. This

experimental value closely agrees with the values obtained from the response surface methodology, confirming

that the RSM using the statistical design of experiments could be effectively used to optimize the process

parameters and to study the importance of individual, cumulative and interactive effects of the test variables in

biosorption.

Each contour plot represents a number of combinations of two test variables with the other variable kept

at its optimal level. The maximum percentage removal of lead is indicated by the surface confined in the smallest



312

curve of the contour plot. The studies of the contour plots also reveal the best optimal values of the process

conditions and are given below:

For chick feathers: biosorbent concentration 0.19g, time 25hrs, pH–7 and for duck feathers biosorbent

concentration 0.15g, time 35hrs, pH–7 which is shown in Fig - 5 to 8.

Fig - 5 Response surface contour plot showing interactive effect of biosorbent concentration

and time on the removal of lead by chick feathers.

Fig - 6 Response surface contour plot showing interactive effect of time and pH on the removal of lead by chick

feathers.



313

The graph was plotted by taking observed and predicted values which shows that both observed and

predicted values are adjacent to the line for both chick and duck feathers which are shown in graphs 1& 2.

Fig - 7 Response surface contour plot showing interactive effect of biosorbent concentration and time on the

removal of lead by duck feathers

Fig – 8 Response surface contour plot showing interactive effect of time and pH on the removal of lead by duck

feathers



314

Observed vs. Predicted Values3 3-level factors, 1 Blocks, 27 Runs; MS Residual=3.648408

DV: % Removal Efficiency

25 30 35 40 45 50 55 60 65 70 75

Observed Values

20

25

30

35

40

45

50

55

60

65

70

75

Pre

dict

ed V

alue

s

Graph - 1 Observed and predicted values for chick feathers

Observed vs. Predicted Values3 3-level factors, 1 Blocks, 27 Runs; MS Residual=4.512952

DV: % Removal Efficiency

30 35 40 45 50 55 60 65

Observed Values

30

35

40

45

50

55

60

Pre

dict

ed V

alue

s

Graph - 2 Observed and predicted values for duck feathers

The critical values obtained for chick feathers are 0.19 grams biosorbent, 24.56 hours, 6.94 pH and for

duck feathers are 0.23 grams biosorbent, 20.17hours, 7.02pH as shown in Table - 4. Therefore, it is apparent that



315

the response surface methodology not only gives valuable information on interactions between the factors but also

leads to identification of feasible optimum values of the studied factors.

Table - 2: Effect Estimates ; Var.:% Removal Efficiency; R-sqr=.98098; Adj:.97091 3 3-level factors, 27 Runs;

Effect Std.Err. t(17) p -95.% +95.% Coeff.

Mean/Interc. 41.3222 0.636694 64.9013 0.000000 -230.44 -60.67 41.32222

(1)Biosorbant

concentration (gm)(L) 28.3889 1.800841 15.7642 0.000000 961.38 1179.54 14.19444

Biosorbant

concentration (gm)(Q) 35.8967 1.559574 23.0170 0.000000 -1959.35 -1630.31 17.94833

(2)Time(hrs)(L) -2.1667 0.900421 -2.4063 0.027771 2.63 5.00 -1.08333

Time(hrs)(Q) 3.1267 0.779787 4.0096 0.000908 -0.05 -0.01 1.56333

(3)pH(L) -0.7422 0.900421 -0.8243 0.421181 -4.76 41.95 -0.37111

pH(Q) 0.8067 0.779787 1.0345 0.315409 -2.45 0.84 0.40333

1L by 2L -16.6683 1.102786 -15.1148 0.000000 -9.50 -7.17 -8.33417

1L by 3L -5.1917 1.102786 -4.7078 0.000203 -37.59 -14.32 -2.59583

2L by 3L -1.9850 1.102786 -1.8000 0.089634 -0.22 0.02 -0.99250

Table - 3: Effect Estimates; Var.:% Removal Efficiency; R-sqr=.91785; Adj:.87437 3 3-level factors, 27 Runs;

Effect Std.Err. t(17) p -95.% +95.% Coeff.

Mean/Interc. 41.70370 0.708124 58.89325 0.000000 40.2097 43.19771 41.70370

(1)Biosorbant

concentration (gm)(L)

22.84444 2.002876 11.40582 0.000000 18.6187 27.07014 11.42222

Biosorbant

concentration (gm)(Q)

16.44444 1.734542 9.48057 0.000000 12.7849 20.10401 8.22222

(2)Time(hrs)(L) 2.60000 1.001438 2.59627 0.018825 0.4872 4.71285 1.30000

Time(hrs)(Q) 0.05556 0.867271 0.06406 0.949671 -1.7742 1.88534 0.02778

(3)pH(L) 0.44444 1.001438 0.44381 0.662780 -1.6684 2.55729 0.22222

pH(Q) 0.45556 0.867271 0.52527 0.606176 -1.3742 2.28534 0.22778

1L by 2L -8.30000 1.226506 -6.76719 0.000003 -10.8877 -5.71230 -4.15000

1L by 3L -2.88333 1.226506 -2.35085 0.031057 -5.4710 -0.29563 -1.44167

2L by 3L -1.01667 1.226506 -0.82891 0.418641 -3.6044 1.57104 -0.50833

Table - 4 Critical values; Variable: % Removal Efficiency Solution: maximum Predicted value at solution: 68.07936

(Chick feathers), 53.18945 (Duck feathers)

Chick feathers Duck feathers

Observed Critical Observed Observed Critical Observed

Biosorbant

concentration (g) 0.10000 0.19098 0.30000 0.10000 0.23246 0.30000

Time(hrs) 15.00000 24.56185 35.00000 15.00000 19.77395 35.00000

pH 6.00000 6.94208 8.00000 6.00000 7.02192 8.00000

CONCLUSION

This work has demonstrated the use of Box–Behnken design for determining the optimum process

conditions leading to the maximum percentage removal of lead from aqueous solutions. Using this experimental

design and multiple regression, the parameters namely, biosorbent concentration, pH and contact time were

studied effectively and optimized with a lesser number of experiments. This methodology could therefore be

successfully employed to study the importance of individual, cumulative and interactive effects of the test variables

in biosorption.



316

ACKNOWLEDGEMENT

The authors express their thanks to the Department of Biotechnology, Bapatla Engineering College, Bapatla

for providing research facilities and valuable guidelines. The first author expresses her gratitude to Prof.

K.R.S.Sambasiva Rao, Director, Centre for Biotechnology, Acharya Nagarjuna University for his encouragement and

support during the period of study.

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