Study Of Biosorbtion Isotherms Biology Essay

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Textile industry is one of the most important industries in Thailand. However wastewater released from dye process create problems to ecosystems and health of people nearby (Boer et al, 2004; Saeed et al., 2009). Among industrial wastewaters, dye wastewater from textile and dyestuff industries is one of the most difficult waters to treat. This is because dyes usually have a synthetic and complex aromatic molecular structure, which makes them more stable and have difficult to biodegrade. The dyes used in the textile industries include several structural varieties such as acidic, reactive, basic, disperse, azo, diazo, anthraquinone based and metal complex dyes. The most commonly used techniques for color removal include coagulation, membrane technologies, flocculation, ozonation, Fenton's reactive, reverse osmosis, cucurbutyril, electrochemical degradation, active carbon. Although the above mentioned methods of physical and / or chemicals have been widely used, but whether there are restrictions, such as high cost, structure of hazardous byproducts and high energy intensive consumtion. Current emphasis on environmental conservation. Therefore the search for a new movement in the treatment of dye contaminated with one of them is the use of biomass as a dye absorption. The use of fungal biomasses as biosorbents for removal of various synthetic dyes from various wastewater (Cing and Yesilada, 2004; Das et al., 2006; Seyis and Subasioglu, 2008) was introduced because of its low cost and environmentally friendly relative to the traditional physicochemical processes (Vijayaraghavan et al., 2007).

2. Objective

The study of biosorbtion isotherms and kinetic model in wastewater treatment is significant as it provides valuable insights into the reaction, mechanism, and pathways of sorption reactions. Therefore, this study was aimed to use the fungal biomass of white rot fungi, Lentinus strigosus in sorption synthetic dyes. The adsorption isotherms and kinetic model equations were used to predict the biosorption mechanism.

3. Research Methodology

3.1. Source of fungus

The white rot fungus, Lentinus strigosus, was obtained from Department of Agriculture, Ministry of Agriculture and Cooperative in Thailand. Stock culture was maintained on Potato Dextrose Agar (PDA) at 4°C until use.

3.2 Synthetic dyes

Two types of dye: Remazol Brilliant Blue R (RBBR) and Remazol Black B (RB5) were obtained from Dystar Thai Company Limited in Thailand.

3.3 Preparation of biomass

The fungus mycelium was grown on fresh PDA and incubated at room temperature (28 - 30 °C) for 5 days. Ten agar plugs (Ø5 mm from the edge of a 5-day-old agar culture) of fungal biomass (Lentinus strigosus) were inoculated in 100 ml Potato Dextrose Broth (PDB) before incubating at room temperature (28 - 30 °C) with shaking for 7 days. After cultivation, the alive biomass was prepared by harvesting and washing three times with distilled water. The dead biomass was prepared through the autoclaving at 121 °C, 1 atm for 20 min. These were ready to be used for further experiments.

3.4 Analysis of synthetic dyes

Concentrations of synthetic dyes solution were determined using a spectrophotometer (JASCO V-530 UV/VIS spectrophotometer) at 592 and 597 nm for RBBR and RB5, respectively.

3.5 Biosorption experimental

The biosorption of synthetic dyes was carried out in 250 ml Erlenmeyer flask containing 100 ml of dyes solution. To ensure the equilibrium, the solution mixtures of 50 mgl-1 dye and 1.0 g of alive or dead biomass at pH 2.0 were incubated at 30 °C with shaking rate of 150 rpm for 6 h on a rotary shaker. The experiments were performed in triplicate. The amount of dyes adsorbed per unit of alive or dead biomass (mg dyes/g biomass biosorbent) was determined using the following expression:

qeq = (1)

Where

qeq = the equilibrium dyes uptake (mg dyes/g biomass weight of alive or dead biomass)

V = the volume of dyes solution (l)

Ci = the initial concentration of dyes in the solution (mg l-1)

C = the residual concentration of dye in the solution at any time (mg l-1)

M = the weight of alive or dead biomass (g)

3.5.1 Sorption isotherm

Langmuir and Freundlich isotherm models were used in the study of adsorption efficiency (Arica and Bayramoglu, 2007; Rachna and Suresh, 2008).

The Langmuir isotherm is based on the homogeneous surface and monolayer adsorption, and is presented by the following equation:

qeq= (2)

where

qmax = the maximum uptake capacities (mg g-1 biosorbent)

Ceq = the equilibrium concentration (mg l-1 solution)

b = the equilibrium constant (l mg-1)

The Freundlich isotherm model is based on heterogeneous surface and multilayer adsorption, and is presented by the following equation:

qeq= (3)

where

KF, n = the Freundlich contants characteristic of the system

3.5.2 Sorption kinetics

In the study of sorption kinetic model, it is very important to know the rate of adsorption for design and evaluate the adsorbent in removing the dyes in water. The kinetic studies were carried out by conducting batch biosorption experiments with different initial dyes concentrations. Samples were taken at different time periods and analyzed for their dyes concentration. The pseudo-first-order Largergren and the pseudo-second order biosorption processes (Zeroual et al., 2006) were applied to the experimental data.

The first-order rate expression of Largergren is shown in the following equation:

log(qeq - qt) = logqeq - k1,adt/2.303 (4)

where

qeq = the amount of adsorbed dye at equilibrium (mg g-1)

qt = the amount of adsorbed dye on the biosorbent at time t (mg g-1)

k1,ad = the rate constant to Largergren first-order biosorption (min-1)

t = time (min)

The pseudo second-order kinetic rate equation is shown in the following equation:

t/q = 1/(k2,adq2eq) + t/qeq (5)

where

k2,ad = the rate constant of second-order biosorption (g mg-1 min-1)

t = time (min)

3. Result

3.1 Biosorption of synthetic dyes

In order to determine the effect of contact time on the dyes sorption capacity of alive and dead biomass, both biosorbents were contacted with 50 mgl-1 dyes solution for various intervals ranging between 20 min and 6 h at 30 °C and pH 2. Fig.1 shows the effect of contact time on dyes sorption capacities of alive and dead fungal biomass. The rapid dyes sorption rate of RBBR and RB5 by both biomass occurred within the first 20 min. The sorption amount of RBBR and RB5 were 65.23 and 64.04%, respectively, by alive biomass, and 82.69 and 84.80%, respectively, by dead biomass. While the equilibrium of RBBR and RB5 sorption system were established in 90 and 120 min for dead and alive biomass respectively.

Fig.1. Effect of contact time on synthetic dyes biosorption capacities of alive and dead fungal biomass

3.2 Sorption Isotherms

The adsorption isotherms indicate how the adsorption molecules distribute between the fungal biomass and dyes molecule when the adsorption process reaches an equilibrium state.

b

a

Fig. 2. Langmuir (a) and Freundlich (b) isotherms of RBBR and RB5 on alive and dead fungal biomass

Fig. 2 shows the Langmuir and Freundlich plots of RBBR and RB5 sorption onto fungal biomass. Table 1 shows the comparisons between Langmuir and Freundlich isotherms. The experimental data fitted well with the Langmuir equation with as high correlation coefficients (r 2) as 0.999. Therefore, the dyes adsorption onto biomass was consistent with strong monolayer sorption. With Langmuir isotherms, the maximum adsorption capacities, qmax, of RBBR and RB5 were 16.12 and 15.15 mg g-1, respectively, by alive biomass, and 66.66 and 29.41 mg g-1 respectively, by dead biomass.

Table 1. Isotherm model constants and correlation coefficients for adsorption of RBBR and RB5 by alive and dead fungal biomass

Biosorbent

Exp.

Langmuir isotherm model

Freundlich isotherm model

qmax(mg g-1)

qmax(mg g-1)

b (l mg-1)

r2

KF

1/n

r2

Alive biomass

RBBR

RB5

15.87 ± 0.58

14.85 ± 2.63

16.12

15.15

0.095

0.103

0.999

0.999

4.45

4.12

0.203

0.207

0.919

0.916

Dead biomass

RBBR

RB5

64.61 ± 0.80

28.39 ± 1.53

66.66

29.41

0.112

0.129

0.999

0.999

8.76

7.61

0.387

0.216

0.893

0.948

The Langmuir constant adsorption value (RL) can be used to predict whether a sorption system is favourable or unfavaourable. Since the RL values were within the nature of the adsorption process as given below table 2 (Anjaneya et al., 2009; Saeed et al. 2009). The calculated by the following equation:

RL = (6)

Where

b = the Langmuir constant (l mg-1)

C0 = the initial dyes concentration (mg l-1)

Table 2. The Langmuir constant adsorption value (RL)

RLvalue

Nature adsorption process

RL>1

RL= 1

0 <RL<1

RL= 0

Unfavorable

Linear

Favorable

Irreversible

The RL values for sorption of RBBR and RB5 are shown in Fig.3 and table 3. The average values of RL at different initial dye concentration was found to be 0.066 and 0.061 respectively, for alive biomass and 0.057 and 0.050 respectively, for dead biomass respectively, indicating that the adsorption of dyes by alive and dead fungus biomass was a favorable process.

Fig. 3 Value of Langmuir constant adsorption (RL) for the sorption of RBBR and RB5 by alive and dead fungus biomass

Table 3. dyes diffusion rate parameter and diffusion coefficient at different initial dye concentration

Initial dye concentration

The value of RL

RBBR

RB5

alive biomass

dead biomass

alive biomass

dead biomass

50

70

90

100

300

500

700

900

1000

0.1739

0.1307

0.1047

0.0952

0.0338

0.0206

0.0148

0.0115

0.0104

0.1515

0.1131

0.0902

0.0819

0.0289

0.0175

0.0125

0.0098

0.0088

0.1626

0.1218

0.0973

0.0884

0.0313

0.0190

0.0136

0.0106

0.0096

0.1342

0.0997

0.0793

0.0719

0.0251

0.0152

0.0109

0.0085

0.0076

3.3 Sorption kinetics

To investigate the sorption kinetics of RBBR and RB5 by the fungal biomass, the constants of dyes sorption were calculated using the pseudo-first and pseudo-second order equation. For evaluation of RBBR and RB5 biosorption, the plot of ln(qe - qt) versus time and t/qt versus time were used and displayed as data shown in Fig. 4 and Table 4.

a

b

Fig. 4 Pseudo-first kinetics model (a) and Pseudo-second kinetics model (b) of RBBR and RB5 on alive and dead fungal biomass

Table 4 Theoretically determined constants and experimental values of kinetic model for adsorption of RBBR and RB5 by alive and dead fungal biomass

Biosorbent

Exp.

Theoretical values

First-order kinetic model

Second-order kinetic model

qeq

(mg g-1)

qeq

(mg g-1)

k1,ad

(min-1)

r2

qeq

(mg g-1)

k2,ad

(mg g-1min-1)

r2

Alive biomass

RBBR

RB5

4.79

4.88

1.48

3.48

0.037

0.039

0.951

0.971

4.93

5.08

0.027

0.019

0.999

0.999

Dead biomass

RBBR

RB5

4.89

4.97

0.26

0.29

0.025

0.039

0.940

0.926

4.95

5.05

0.056

0.059

1.000

0.999

From Table 4, the pseudo-second order kinetic model provided better correlation of all experimental data than the pseudo-first order kinetic model. In addition, all the qeq calculated using the second-order kinetic model were closer to the experimental values than using the first-order kinetic model.

4. Discussion and Conclusion

The present study shows that the biomass of Lentinus strigosus was an effective biosorbent for the adsorption of RBBR and RB5 from aqueous solution. The effect of contact time on synthetic dyes biosorption capacities of alive and dead fungal biomass. It was found that the dye adsorption experiments at the same time, the dead biomass adsorbed RBBR and RB5 than alive biomass. Accoding to Gallagher et al. (1997) and Fu and Viraraghavan (2002) reported the biosorption of Reactive Red 158 and Congo Red by Aspergillus niger. It was found that the dye sorption by dead biomass was better than that by alive biomass. The preparation of fungal biosorbent by an autoclave process increased the sorption capacity of the fungal biomass by disrupting the fungal structure. According to Arthur et al. (2007) reported the Tametes versicolor reveals the porosity and surface texture. The fibrous nature of the wall components was found only in the alive biomass. Dead biomass is likely to be caked by autoclave treatment, implying that the physical strength of hypae of the fungus was weak. Therefore, the autoclave process may also facilitate a cementing effect of fungus wall componants, thus changing fibrous hypae to from the caked morphology of the wall surface. This effect might cause an increase in surface area and porosity of the fungus biomass, and thus latent sites, consequently increasing the dye adsorption.

The efficiency of adsorption isotherms and kinetics model has been developed and fitted for the sorption of synthetics dyes onto biomass of White rot fungus, Lentinus strigosus. The results show that the sorption of synthetics dyes onto biomass can be described by a Langmuir isotherm and pseudo-second-order-model. The dyes adsorption are consistent with strong monolayer sorption and the assumption that the rate-limiting step may be chemical sorption involving valency forces though exchange or sharing of electrons between the white rot fungal biomass and dyes molecule. (Iqbal and Saeed, 2007; Ong et al., 2010).

5. Suggestion

The study showed that the biomass of Lentinus strigosus reduced synthetic dyes effectively, but that will be used for actual industrial scale should study the situation real wastewater from the production process to get the conditions removed dyes have a suitable and effective for a maximum dye absorption.

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