Simultaneous removal of Cr(VI) and phenol from binary solution using Bacillus sp. immobilized onto tea waste biomass

Journal of Water Process Engineering 6 (2015) 1–10

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Simultaneous removal of Cr(VI) and phenol from binary solution using Bacillus sp. immobilized onto tea waste biomass Ankur Gupta ∗ , Chandrajit Balomajumder Department of Chemical engineering, Indian Institute of Technology Roorkee, India

a r t i c l e

i n f o

Article history: Received 3 December 2014 Received in revised form 1 February 2015 Accepted 2 February 2015 Keywords: Phenol Chromium(VI) Tea waste biomass Bacillus sp. Multicomponent adsorption isotherms Kinetics

a b s t r a c t In this investigation, simultaneous Cr(VI) reduction and phenol degradation from contaminated water using Bacillus sp. immobilized onto the surface of tea waste biomass have been studied in a batch reactor. It was observed that Bacillus sp. utilized phenol as a carbon source for Cr(VI) reduction. Optimal conditions were achieved at a biomass dosage of 15 g/L with an initial concentration of 100 mg/L of Cr(VI) and 50 mg/L of phenol. The maximum uptake capacity of Cr(VI) and phenol onto tea waste biomass surface was 741.389 mg/g and 7.761 mg/g, respectively. The equilibrium condition was reached after 27 h for phenol and 48 h for Cr(VI). Multicomponent isotherm models were used to determine the adsorption mechanism for both Cr(VI) reduction and phenol degradation. Non-modified competitive Redlich–Peterson was found to be the best fit for Cr(VI) sorption while extended Langmuir was followed in the case of phenol degradation. Moreover, the experimental results revealed that both Cr(VI) and phenol were well described by the pseudo second-order model. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction With the rapid growth in industrialization, the contaminated waste water discharged from industries such as electroplating, leather tanning, textile, paints and pigments contains increasing levels of Cr(VI) and organic matter like phenol [1]. Chromium exists in two stable oxidation states, i.e., Cr(III) and Cr(VI), and Cr(VI) is more toxic and mobile as compared to Cr(III). Cr(VI) is the most mutagenic and carcinogenic to the living organism [2]. As per the guidelines recommended by the World Health Organization (WHO), the maximum permissible limit of Cr(VI) in drinking water is 0.05 mg/L [3]. According to the US environmental protection agency, phenol is a major pollutant and its permissible limit for discharge in waste water is 0.005 mg/L [4]. Long-term exposure of phenol may cause severe health effects on living beings. Phenol is toxic to the nervous system, heart, kidneys, and liver [5]. Several distinctive techniques used for the remediation of heavy metal ions and organic matter includes precipitation/coagulation [6], chemical oxidation [7], biodegradation [8], adsorption [9], ion exchange [10], membrane processing [11], electrolytic methods [12] etc. Therefore there is a need for the development of methods which are cost effective and lead to less generation of secondary waste. A

∗ Corresponding author. Tel.: +91 8057410290. E-mail addresses: [email protected] (A. Gupta), [email protected] (C. Balomajumder). http://dx.doi.org/10.1016/j.jwpe.2015.02.004 2214-7144/© 2015 Elsevier Ltd. All rights reserved.

microorganism is used as biosorbent for the removal of heavy metals and organic compounds [14]. Both live and dead microbial cells are used to transform or adsorb heavy metals and their products and can be a highly efficient bioaccumulator [15]. Cr(VI) and its copollutants such as phenol, naphthalene, and trichloroethylene discharged from various industries commonly contaminate groundwater aquifers, lake and river sediments and soil. Therefore, simultaneous removal of Cr(VI) and phenol have attained a great attention in wastewater treatment processes [16]. Heavy metals combined with organic matter form complexes and hence increase the removal of both pollutants [17]. The aromatic compounds such as phenol are used as electron donors for microbial reduction of Cr(VI) [18]. The possible reason behind the increase in removal of Cr(VI) in the presence of phenol is that the kinetics of Cr(VI) reduction is improved by combining the Cr(VI) reduction to other energy yielding reactions such as phenol degradation [13]. Few works are reported for simultaneous reduction of Cr(VI) and biodegradation of phenol by the use of suitable consortium of bacteria [13,19–21]. The aim of this study is (i) to determine optimum process parameters viz., pH, biosorbent dose, contact time for simultaneous removal of phenol and Cr(VI) by the use of single bacterium Bacillus sp. immobilized or supported onto the surface of tea waste biomass. (ii) To determine the applicability of multicomponent equilibrium models. (iii) To study the kinetics of simultaneous biosorption of Cr(VI) and biodegradation of phenol to determine best fit kinetic models.

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A. Gupta, C. Balomajumder / Journal of Water Process Engineering 6 (2015) 1–10

2.25

Nomenclature

Ci Ct Ce V W qe MPSD ARE qe,i exp qe,i cal N P RL KL KF n KRP aRP ˇ Qmix Qo Qo,i Ce,i qe,i KF,i xi , yi , zi k1 k2 kid

Specific uptake capacity of adsorbent (mg/g of adsorbent) Initial pollutant concentration (mg/L) Pollutant concentration at time t (mg/L) Equilibrium concentration (mg/L) Volume of solution L Mass of adsorbent used (g) Specific uptake of adsorbent at equilibrium (mg/g of adsorbent) Marquardt’s percent standard deviation Average relative error Experimental specific uptake (mg/g) Calculated specific uptake (mg/g) Number of observations in the experimental isotherm Number of parameters in the regression model Separation factor Langmuir constant (L/g) Constant in Freundlich model (mg/g)/ (mg/L)1/n Constant in Freundlich model Redlich–Peterson isotherm constant (L/g) Redlich–Peterson isotherm constant (L/mg)␤ Redlich–Peterson isotherm exponent Adsorption capacity of one adsorbate in mixture (mg/g) Adsorption capacity of one adsorbate when present alone (mg/g) Constant in modified Langmuir model for ith component (mg/g) Concentration of ith component in the binary mixture at equilibrium (mg/g) Amount of ith component adsorbed per gram of adsorbent at equilibrium (mg/g) Constant in extended Freundlich constant for ith component (mg/g)/(mg/L)1/n Constant in extended Freundlich model for the ith component Rate constant in pseudo first order model (h−1 ) Rate constant of pseudo-second order kinetic model (mg/g h−1 ) Intraparticle diffusion constant (mg/g h−0.5 )

OD at 600 nm

q

2 1.75 1.5

1.25 1

0.75 0.5

0.25 0 0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 Contact time, h Fig. 1. Growth of Bacillus sp. with time.

2.2. Growth and cultivation of Bacillus sp. The Bacillus sp. was grown in a liquid nutrient medium containing all the components as described above in nutrient medium except agar. The nutrient medium was incubated in a 250 mL flat bottom flask with a working volume of 100 mL at 120 rpm and 37 ◦ C for 30 h. The cultivated cells of Bacillus sp. were centrifuged at 10,000 rpm for 10 min. The pellet formed at the bottom of the centrifuge tube was washed with distilled water and its OD was noted at 600 nm at a fixed interval of time of 3 h in the UV spectrophotometer. Maximum growth of bacterial cells was obtained at 30 h; beyond this point the bacterium starts to decline, as shown in Fig. 1. 2.3. Preparation of solutions All chemicals used for experimentation purpose, including potassium dichromate and phenol, were AR grade having more than 99% purity. Stock solutions of Cr(VI) and phenol were prepared by dissolving known amounts of phenol and potassium dichromate in 1 L of distilled water. To avoid photo-oxidation of phenol, stock solution was stored in a brown glass bottle [25]. Various initial concentrations of test solutions of phenol and Cr(VI) were prepared by diluting the stock solutions. For multicomponent tests, a solution of phenol and Cr(VI) was prepared by diluting their respective stock solutions and mixing them in the desired proportion. Based on industrial wastewater, a 2:1 ratio of Cr(VI) and phenol were taken for conducting the present experiments. 2.4. Preparation of tea waste biomass

2. Materials and methods 2.1. Bacterial strain and medium The microorganism Bacillus sp. MTCC No. 3166 was purchased from IMTECH Chandigarh. The Bacillus sp. was stored at 4 ◦ C in nutrient agar medium containing beef extract 1.0 g, yeast extract 2.0 g, peptone 5.0 g, NaCl 5.0 g, agar 15 g in 1:l of distilled water. The pH of nutrient medium was 7.0. All chemicals used for the preparation of nutrient media were of analytical grade. All experiments were carried out at a working volume of 100 mL. Before starting each experiment, nutrient medium used for the growth of microorganisms was sterilized at 121 ◦ C and 15 psi for 30 min. After that, Bacillus sp. was enriched in a liquid nutrient medium by transferring one loop of bacterial cells from the agar slant to 100 mL of nutrient medium in a 250 mL flat bottom flask. For the growth of Bacillus sp. in nutrient medium, it was kept in an incubator cum shaker at 37 ◦ C and 120 rpm [22–24].

Tea waste biomass was collected from a local tea stall located near the campus of IIT Roorkee. Soluble sugar and dirt present in tea waste biomass was removed by boiling in distilled water for about 30 min. After that, washing and cooling was carried out with distilled water and dried at 50 ◦ C in a hot air oven for 24 h. Further, the dried biomass was sieved to the desired particle size of 0.5–2 mm and then sterilized in an autoclave at 121 ◦ C and 15 psi [26]. 2.5. Analytical methods The concentration of Cr(VI) and phenol in the supernatant liquid after centrifugation was determined by using a double UV spectrophotometer (Hach DR-5000). The concentration of Cr(VI) in the supernatant was determined at the wavelength of 540 nm by reaction with 1,5-diphenylcarbazide. The residual concentration of phenol was determined at 570 nm by 4 amino antipyrene method [27,28].

A. Gupta, C. Balomajumder / Journal of Water Process Engineering 6 (2015) 1–10

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Table 1 Surface properties of tea waste biomass. Biosorbent

BET surface area (m2 /g)

Monolayer volume (cm3 /g)

Total pore volume (m3 /g)

Unloaded tea waste biomass Tea waste biomass after immobilization with Bacillus sp. Tea waste biomass after simultaneous biosorption and biodegradation of Cr(VI) and phenol

22.658 16.896 3.456

4.387 1.567 0.678

0.0255 0.021 0.00345

2.6. Cr(VI) reduction and phenol degradation experiment Batch experiments on Cr(VI) reduction and phenol degradation were carried out in a 250 mL flat bottom flask containing 100 mL liquid nutrient medium as described in Section 2.1. All the glassware and flasks containing 100 mL of nutrient medium were autoclaved at 121 ◦ C and 15 psi. After cooling the nutrient medium at room temperature, one loop of bacterial cells from agar slants was transferred to the previously sterilized nutrient media in the laminar flow chamber (Rescholar Equipment M. No. RH-57-02) and then kept in an orbital cum incubator shaker (Metrex, MO-250, India) for 30 h at 37 ◦ C and 120 rpm for acquiring maximum growth of bacterial cells. After acquiring maximum growth of bacterial cells in the nutrient medium, a known quantity of tea waste biomass was added to form a biofilm onto the surface of tea waste biomass by keeping it in in an incubator shaker for another 24 h. After attaining maximum growth of bacterial cells, the desired initial concentration of phenol and Cr(VI) was added to the suspension culture and their concentration in supernatant were measured at definite intervals of time until optimum conditions were achieved. Due to the possibility of volatilization of phenol during the experiment, control experiments were carried out at the same operating conditions [29,30]. The percentage removal of phenol and Cr(VI) was calculated by the following equation: Percentage removal =

Ci − Ct × 100 Ci

(1)

The adsorption capacity, qe (mg/g) of phenol and Cr(VI) was calculated as follow: Equilibrium adsorption capacity, qe (mg/g) =

(Ci − Ct ) V W

(2)

3. Results and discussion 3.1. Characterization of tea waste biomass 3.1.1. SEM scanning electron micrograph, EDX and BET surface area analysis of biosorbent The morphology and composition of tea waste biomass was obtained by SEM and EDX analysis. It is clear from SEM analysis (Fig. 2a) that before simultaneous biosorption and biodegradation the biomass surface was homogeneous and porous, but after immobilization of Bacillus sp. the biomass surface was uniformly covered by a layer of biofilm (Fig. 2b). After simultaneous sorption and biodegradation of Cr(VI) and phenol, the sorbent surface became rough and less porous than before simultaneous biosorption and biodegradation of Cr(VI) and phenol (Fig. 2c) [31,32]. This was also confirmed by the surface properties of tea waste biomass before and after adsorption given in Table 1. (BET) surface area and total pore volume of the unloaded tea waste biomass after immobilization with Bacillus sp. and after simultaneous biosorption and biodegradation of Cr(VI) and phenol was calculated using a surface area analyzer ASAP 2010 Micrometrics, USA. Unloaded tea waste biomass has a very high surface area (22.658 m2 /g), which shows that it is a potential biosorbent for the removal of Cr(VI) and phenol. Table 1 shows that after after simultaneous biosorption

Fig. 2. SEM photograph of tea waste biomass (a) before adsorption (b) after immobilization with Bacillus sp. (c) after simultaneous biodegradation and bioaccumulation of phenol and Cr(VI).

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Fig. 3. EDX of tea waste biomass (a) before adsorption (b) after biodegradation and bioaccumulation of phenol and Cr(VI).

and biodegradation of Cr(VI) and phenol, the surface area (m2 /g), monolayer volume (cm3 /g) and total pore volume (m3 /g) were very much less in comparison to unloaded material after immobilization with Bacillus sp. which confirms the simultaneous biosorption and biodegradation of Cr(VI) and phenol. EDX analysis was carried out to give the elemental composition of the samples. Fig. 3a shows EDX analysis of tea waste biomass immobilized with Bacillus sp. before biosorption. The results revealed that the sharp peaks of elements like C, O and N, and also smaller peaks such as Na, Si and Ca were observed. After simultaneous biosorption and biodegradation of Cr(VI) and phenol, elemental compositions in weight% of peak of C, N, O and Ca as obtained from EDX analysis were different from before biosorption (Fig. 3b). Weight% of C, O, N and Ca changed from 54.16% to 52.23%, 37.94% to 34.52%, 6.23% to 4.88% and 0.79% to 3.5% before and after adsorption, as noted from the EDX results, and the weight% of Cr(VI) was found to be 4.87% after adsorption. The weight% of other elements such as Si, Na, becomes negligible after simultaneous adsorption of Cr(VI) and phenol, as shown in Tables 2a and 2b, respectively.

3.1.2. FTIR of biosorbent before and after adsorption The FTIR spectrum of tea waste biomass immobilized with Bacillus sp. before adsorption and after adsorption is shown in Fig. 4. The strong band at 3432.00 cm−1 shows the vibrations of

Table 2a Various elements present onto the tea waste biomass surface before adsorption. Elements

Weight%

Atomic%

Net Int.

Error%

CK NK OK Na K Si K Ca K

54.16 6.23 37.94 0.58 0.29 0.79

61.09 6.03 32.12 0.34 0.14 0.27

234.47 4.73 100.63 3.94 3.74 4.72

5.68 27.68 11.16 66.97 63.31 60.24

N H and O H functional groups. The bands at 3000 − 2750 cm−1 were assigned to the C H stretching mode, which represents the aliphatic nature of biosorbent. The adsorption bands at around 1742.23 − 1225.60 cm−1 were characteristics of C C in aromatics Table 2b Various elements present on the tea waste biomass surface after adsorption according to EDX spectra. Elements

Weight%

Atomic%

Net Int.

Error%

CK NK OK Ca K Cr K

52.23 4.88 34.52 3.5 4.87

61.81 4.95 30.67 1.24 1.33

142.39 2.32 58.28 13.73 9.62

6.25 41.27 11.87 18.44 21.77

A. Gupta, C. Balomajumder / Journal of Water Process Engineering 6 (2015) 1–10

5

110 100 90 % Removal

80 70 60 50

Cr(VI)

40

Phenol

30 20 10 0 0

0.25 0.5 0.75

1

1.25 1.5 1.75

2

2.25 2.5

Adsorbent dose, g Fig. 6. Effect of quantity of tea waste biomass immobilized with Bacillus sp. on biosorption of Cr(VI) and phenol. Fig. 4. FTIR spectrum of tea waste biomass immobilized with Bacillus sp. before adsorption and after simultaneous adsorption of Cr(VI) and phenol.

rings. Peaks at 1500 − 1000 cm−1 attributed to C O group on the surface of biomass [33,34]. Furthermore, peaks at 1000 − 500 cm−1 indicate the presence of silica SiO2 . From the FTIR spectrum before and after simultaneous removal of phenol and Cr(VI), it clearly shown that there is a change in vibration frequency ranging from 3000 − 2750 cm−1 and 1750 − 1000 cm−1 which indicates simultaneous biosorption and biodegradation of Cr(VI) and phenol was taken place.

that, at low pH, more hydrogen ions compete with metal ions at each binding site resulting in low uptake; therefore, maximum percentage removal usually occurred between pH 5 and 9. It was reported in literature that at a low pH value Cr(VI) was present in the form of Cr2 O7 2− and HCrO4 − but at a higher pH value CrO4 2− ions prevailed in the solution. Uptake of these metal ions is dependent upon the affinity with the biosorbent [14]. In contrast to Cr(VI) adsorption, phenol adsorption was due to Van der Waals forces and – interaction between the phenyl ring and the bacterial cells on the surface of tea waste biomass [28].

3.2. Process parameter optimization 3.2.1. Effect of pH For multi-component systems, pH is an important parameter. pH reflects the nature of biosorption mechanism on the bacterial cell surface and it is related to the physico-chemical interaction of species in binary solution [9,14]. pH value also affects the property of functional groups such as carboxylate, phosphate and amino groups [18]. Both phenol and Cr(VI) have different pH optima according to their chemistry of adsorption onto the surface of biosorbent. For a binary mixture of Cr(VI) and phenol, the same pH binding profile could be due to the behavior of chemical interaction of each component with the microbial cell immobilized on the surface of biosorbent. The variation of percentage removal of each component with pH is shown in Fig. 5. Maximum percentage removal of both components was obtained at pH 5. It was observed

100 90 % Removal

80 70 60 50

Phenol

40

Cr(VI)

30 20 1

2

3

4

5 pH

6

7

8

Fig. 5. Effect of varying pH on percentage removal of Cr(VI) and phenol.

9

3.2.2. Effect of biosorbent dose immobilized with Bacillus sp. Tea waste biomass immobilized with Bacillus sp. was used as biosorbent for the bioaccumulation and biodegradation of Cr(VI) and phenol. Maximum uptake capacity of phenol and Cr(VI) onto the surface of bacterium immobilized biomass from the binary mixture was found to be 15 g/L. The percentage removal of both phenol and Cr(VI) was rapid and increases with the increase in biomass quantity at initial stage; however, it gradually becomes constant. The increase in percentage removal with the increase in biomass dose was due to an increase in surface area as well as a number of possible vacant active sites available for adsorption onto the surface of Bacillus sp. immobilized biosorbent [35,36]. After reaching optimum dose, the percentage removal of both phenol and Cr(VI) becomes constant, this could be due to overlapping of biomass dose [37]. The tea waste biomass dose immobilized with Bacillus sp. was varied from 2.5 g/L to 20 g/L, but after 15 g/L biomass dose the percentage removal of both phenol and Cr(VI) becomes constant, as shown in Fig. 6. Hence, 15 g/L is considered as an optimum biomass dose. Further equilibrium and kinetic studies were carried out at this optimum dose. 3.2.3. Effect of contact time Contact time is an important parameter in achieving equilibrium conditions. At equilibrium, there is no change in concentration of adsorbate on the surface of the biosorbent as well as in solution. The time required to reach equilibrium for phenol is less than that of Cr(VI) because phenol is utilized as a carbon source for the reduction of Cr(VI) and their lesser concentration in binary mixture. Equilibrium conditions for Cr(VI) and phenol were achieved at 48 h and 24 h, respectively. From Fig. 7, it was observed that initially the percentage removal of both Cr(VI) and phenol was very fast and then gradually increases until at a certain point becomes constant. This is due to the fact that initially there is a high concentration

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A. Gupta, C. Balomajumder / Journal of Water Process Engineering 6 (2015) 1–10

100

(a) 110

90

100

70 60 50

Cr(VI)

40

Phenol

30 20 10

% Removal

% Removal

80

90 80 70 60

0 0

3

6

9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 Contact time, h

50 50

100 150 200 250 300 350 400 450 500 Initial conc (mg/L)

Fig. 7. Effect of contact time on percentage removal Cr(VI) and phenol.

gradient between the bulk liquid and the biosorbent surface; after that, the concentration gradient decreases [38].

(b) 100

3.2.4. Single and dual biosorption of Cr(VI) and phenol The maximum biosorption of Cr(VI) and phenol using Bacillus sp. biofilm supported on tea waste biomass was 14.0755 mg/g and 7.6201 mg/g, respectively, for the single component solution. For the multicomponent solution of phenol and Cr(VI), the maximum adsorption capacity of Cr(VI) and phenol was 741.389 mg/g and 7.7608 mg/g, respectively. This is due to fact that uptake of Cr(VI) was increased in the presence of organic compounds. The reason behind this fact is that the kinetics of Cr(VI) reduction was improved by combining Cr(VI) reduction to other energy yielding reactions such as phenol degradation [1,39]. Results show that phenol is used as a carbon source, due to which Cr(VI) reduction increases. Initial concentration of Cr(VI) and phenol was varied from 100 to 500 mg/L and 50 to 250 mg/L. The rate of Cr(VI) reduction and phenol degradation was observed to be faster during an initial interval of time after which it becomes slower as shown in Fig. 8a and b, respectively.

80

% Removal

90

70 60 50 40 25

75 100 125 150 175 200 225 250 Initial conc (mg/L)

Fig. 8. Effect of initial concentration in multicomponent system (a) Cr(VI) (b) phenol. Table 3a Parameters of single component adsorption isotherms. Isotherm models

Parameter

Langmuir

Qo KL RL MPSD R2 P value

14.076 6.953 0.00144 18.052 0.829 1.78 × 10−4

Freundlich

KF n MPSD R2 P value

8.82 9.049 13.438 0.864 2.84 × 10−4

3.606 4.457 7.398 0.93 2.78 × 10−5

Redlich–Peterson

KRP aRP ˇ MPSD R2 P value

1471.87 162.881 0.894 13.431 0.863 2.53 × 10−4

55518.1 14641.3 0.789 7.847 0.915 2.98 × 10−5

4. Equilibrium and kinetic modeling for simultaneous removal of Cr(VI) and phenol 4.1. Equilibrium modeling The adsorptive equilibrium data for the adsorption of phenol and Cr(VI) on tea waste biomass was analysed using the solver function and regression function of Microsoft Excel 2010. Mono and multicomponent adsorption isotherm were applied to the experimental data for the single and multicomponent solutions of phenol and Cr(VI). Mono component isotherms such as Langmuir, Freundlich and Redlich–Peterson model were applied for single component systems [40]. Non modified competitive Langmuir, Modified competitive Langmuir, extended Langmuir, extended Freundlich and competitive non modified Redlich–Peterson model were applied for multicomponent systems [14,25,41]. The mono component adsorption isotherm constant is given in Table 3a, and the multicomponent adsorption isotherm constant was calculated using single component data as given in Table 3b. For mono component systems, the Freundlich model and Redlich–Peterson models are suitable for both phenol and Cr(VI), whereas for multicomponent systems non-modified competitive Redlich–Peterson and extended Langmuir were very suitable for Cr(VI) and phenol, which is confirmed by lower MPSD and high R2 values. According to Carmona et al. [42], the rejection of the null hypothesis is statistically significant when P < 0.05. Here P values given in Tables 3a and 3b for single and multicomponent adsorption isotherm models respec-

50

Cr(VI)

Phenol 7.62 1.229 0.016 24.369 0.764 8.9 × 10−4

tively are significant except the extended Freundlich model for phenol having high MPSD and low R2 values. Mono component adsorption model constant values express the surface properties and affinity of biosorbent for each solute. KF and n Freundlich isotherm constants determine the adsorption capacity of biosorbent; the higher the value of n, the higher the affinity of solute for the biosorbent and the higher the adsorption capacity [1]. Here the Freundlich constant n for both Cr(VI) and phenol was greater than 1 and lay in the range of 2–10, indicating a more favorable adsorption [25]. The Redlich–Peterson exponent ˇ lies in the range of 0–1 suggesting good biosorption of Cr(VI) and biodegradation of phe-

A. Gupta, C. Balomajumder / Journal of Water Process Engineering 6 (2015) 1–10 Table 3b Parameters of multicomponent adsorption isotherms. Isotherm model

Parameter

Cr(VI)

Non-modified competitive Langmuir: qe,i =

Phenol

Non-modified Langmuir

MPSD R2 P value

40.24 0.835 0.037

88.886 0.534 0.042

Modified Langmuir

nj MPSD R2 P value

41.852 52.492 0.634 0.01

14.136 49.451 0.679 0.0018

Extended Langmuir

Extended Freundlich

Non modified Redlich–Peterson

Qo , i bi MPSD R2 P value

741.389 0.00037 44.264 0.781 1.75 × 10−3

xi yi zi MPSD R2 P value

4.997 5.991 5.888 50.959 0.742 8.76 × 10−3

KRP aRP ˇ MPSD R2 P value

19.746 1.769 0.822 40.951 0.828 6.47 × 10−4

1 1 + KL Ci

7.761 0.076 9.269 0.922 5.87 × 10−5

1/n

Redlich Peterson : qeq =

(5) KRP Ceq ˇ

1 + aRP Ceq

(6)

Competitive non nodified Redlich–Peterson model qeqi =

KRPi Ceqi

1+

N

ˇ a C j j=1 RPj eqj

qe,i =





N

(8)

bC j=1 j e,j

(Qo,i bi Ce,i /nj ) 1+

N



(9)

b (C /nj j=1 j e,j

Extended Langmuir: qe,i =



Qo,i bi Ce,i 1+



N

(10)

bC j=1 j e,j

KF,i C



(7)

qe,j =



1/ni +xi

e,i

x Z C i +yi C i e,i



6.069 11.693 0.049 17.112 0.872 5.84 × 10−4

(4)

Freundlich : qe = KF Ce

1+

qe,i =

0 1 unfavorable adsorption, RL = 1 linear adsorption, RL = 0 irreversible adsorption. Here separation factor RL lies in the range of 0–1 as given in Table 3a for both phenol and Cr(VI) and decreases with increase in concentration, indicating favorable adsorption at lower concentration. In literature, it is reported that the kinetics of Cr(VI) reduction is improved by coupling of Cr(VI) reduction to other energy yielding reactions such as phenol degradation [1,18]. Here, the adsorption capacity of the biosorbent for both phenol and Cr(VI) was found to be more in multicomponent systems in comparisons to when present alone, therefore a synergism effect is exhibited for the binary biosorption of phenol and Cr(VI) [25]. Cr(VI) and phenol binary sorption on the surface of immobilized tea waste biomass has not been reported so far, hence the generated data from the present experiments could not be compared with the literature. The equations of mono and multi component adsorption isotherm are given below: KL Ce 1 + KL Ce

Qo,i bi Ce,i

ExtendedFreundlich: 

0.328 9.999 7.999 106.904 0.433 0.053

(3)

Langmuir : qe = Qo



Modified competitive Langmuir:

nol [14]. The mono layer Langmuir constant KL and Qo represents monolayer saturation at equilibrium and the affinity of binding of solute on the surface of tea waste biomass. The magnitude of Qo and b shows that the amount of Cr(VI) ions per unit weight of biosorbent to form complete monolayer was higher for Cr(VI). The parameters of Langmuir isotherm were used to derive RL (the separation factor) which is used to explain the feasibility of the biosorption process [43]: RL =

7

1/nj +xj

KF,j Ce,j x

 (11)

e,j

Z

Ce,jj + yj Ce,ij

 

(12)

4.2. Kinetic modeling After equilibrium conditions are achieved, the percentage removal of compounds becomes constant. Kinetic modeling determines the mechanism of biosorption i.e., whether the process is physisorption or chemisorption [44]. Adsorption capacity depends upon the adsorption of adsorbate on the surface of biosorbent. Therefore, kinetic modeling generates information on use of adsorption capacity of the biosorbent. Various kinetic models are reported in literature [45]. Kinetic models such as pseudo first order, pseudo second order and intraparticle diffusion model have been used in the present study [46,47]. Pseudo first order : log (qe − qt ) = logqe − Pseudo second order :

k1 t 2.303

t 1 t = + qt qe k2 q2e

Intra particle diffusion model : qt = kid t 1/2 + I

(13) (14) (15)

The experimental data for binary biosorption and biodegradation of Cr(VI) and phenol using Bacillus sp. supported onto tea waste biomass are applied to various kinetic models such as pseudo first order, pseudo second order and intra particle diffusion kinetic model as shown in Fig. 9a–c, respectively. Kinetic model parameters for Cr(VI) and phenol are shown in Tables 4a and 4b, respectively. Kinetic data agreed well with a pseudo second order model for both phenol and Cr(VI), as compared to a pseudo first order model, which was confirmed by lower, ARE and high R2 values. All the kinetics models are statistically significant for both Cr(VI) and phenol as P < 0.05 in Tables 4a and 4b, respectively. Therefore, binary biosorption of Cr(VI) and phenol on the surface of tea waste biomass is due to chemisorption. A comparative plot of experimental and calculated values of adsorption capacity qt (mg/g) was plotted for both Cr(VI) and phenol, and is shown in Fig. 10a and b respectively. It is clear that experimental value for both Cr(VI) and phenol is in good agreement with a pseudo second order model. To understand the nature of diffusion, an intraparticle diffusion model was applied to the experimental data of binary biosorption of Cr(VI) and phenol. According to the intraparticle diffusion model, a plot of qt (mg/g) vs. t0.5 was plotted. Applicability of intraparticle diffusion model as a rate controlling step depends upon the plot passing through the origin, but here the plot for both phenol and chromium does

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A. Gupta, C. Balomajumder / Journal of Water Process Engineering 6 (2015) 1–10 Table 4b Parameters of kinetic modeling of adsorption of phenol.

1 0.8 log (qe - qt)

0.6 0.4 0.2 0

-0.2 0 3 6 9 12151821242730333639424548 t, h -0.4 Cr (VI) -0.6 Phenol -0.8

(a) Pseudo I order for Cr (VI) and phenol 8 7 6 t/qt

5 4

Cr (VI)

3

Kinetic Parameters

Phenol

Pseudo-first order K1 qe,cal R2 ARE P value

0.109 4.171 0.892 3.453 0.0013

Pseudo-second order K2 qe,cal R2 ARE P value

0.015 5.698 0.986 2.804 7.48 × 10−5

Intraparticle diffusion model Kid R2 ARE P value

0.794 0.977 3.558 4.89 × 10−7

Phenol

2 1

7

0 0 3 6 9 1215182124273033363942454851 t,h

6

(b) Pseudo II order for Cr (VI) and phenol

qt (mg/g)

5 4

7

qt (mg/g)

6 5 4 3

Cr (VI)

2

Phenol

experimental

3

Pseudo I order

2

Pseudo II order

1 0 0

1

3

6

9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 t, h

0

(a)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 t0.5, h

4.5

(c) Intra particle diffusion model for Cr (VI) and phenol

3.5 qt (mg/g)

Fig. 9. (a) Pseudo I order for Cr(VI) and phenol, (b) pseudo II order for Cr(VI) and phenol, (c) intra particle diffusion model for Cr(VI) and phenol.

4

3

2.5

Table 4a Parameters of kinetic modeling of adsorption of Cr(VI). Kinetic Parameters

Cr(VI)

Pseudo-first order K1 qe,cal R2 ARE P value

0.049 7.026 0.876 4.552 8.81 × 10−7

Pseudo-second order K2 qe,cal R2 ARE P value

0.0038 9.643 0.895 3.854 3.72 × 10−7

Intraparticle diffusion model Kid R2 ARE P value

0.964 0.949 4.957 3.92 × 10−11

Experimental

2

1.5

Pseudo I order

1 0.5 0 0

3

6

9

12

15

18

21

24

27

t, h (b) Fig. 10. comparative plot of experimental and calculated value of qt by pseudo I order and pseudo second order kinetic model for (a) Cr(VI) (b) phenol.

A. Gupta, C. Balomajumder / Journal of Water Process Engineering 6 (2015) 1–10

not pass through the origin which shows that here intraparticle diffusion is not a rate controlling step. 4.3. Validation of model MPSD Marquardt’s percent standard deviation is applied to the validation of equilibrium data given below.

  exp 2   1 n qe,i − qcal e,i MPSD = 100 × N−P

i=1

exp

qe,i

(16)

More accurate estimation of the qe value depends upon a lower MPSD value. The MPSD value should be smaller for the correct estimation of qe . Average relative error (ARE) between the experimental and calculated values was calculated for the validation of the kinetic model. The equation for calculating ARE is given by the following equation [25]

  exp 2   N qe,i − qcal 100 e,i × ARE(%) = i=1

exp

qe,i

N

(17)

For the accurate estimation of qt value, ARE should be smaller. 5. Conclusions Industrial effluents such as from the tannery, textile, electroplating, and alloying industries contain Cr(VI) and phenol as major pollutants. Hence, in this investigation, a biosorption system for simultaneous Cr(VI) reduction and phenol degradation using Bacillus sp. supported on tea waste biomass was designed. The experimental results revealed that this system has a good potential for the removal of Cr(VI) and phenol from the liquid phase. Mono component adsorption isotherm such Langmuir, Freundlich, Redlich–Peterson and multicomponent adsorption isotherm such as Non-modified Langmuir, competitive modified Langmuir, extended Langmuir, extended Freundlich, and competitive non-modified Redlich–Peterson isotherm models were used to predict the equilibrium uptake of phenol and Cr(VI) both singly and in combination. It was found that the entire equilibrium model fitted well with the experimental data in the studied concentration range. However, non-modified competitive Redlich–Peterson and extended Langmuir for Cr(VI) and phenol greed better with the experimental results. It was found that reduction of Cr(VI) was greater in the presence of phenol because phenol acts as a carbon source and electron donor for microbial reduction of Cr(VI). Hence, a multi-component system for the simultaneous removal of phenol and Cr(VI) using Bacillus sp. immobilized tea waste biomass was better than single component biosorption. A synergistic effect was exhibited for the multicomponent system, as the reduction of Cr(VI) was greater in the presence of phenol. Further, the experimental data agreed with a pseudo second-order kinetic model of both phenol and Cr(VI) for multicomponent systems; therefore, chemisorption was the mechanism of biosorption. Acknowledgements The author gratefully acknowledges financial support provided by the MHRD assistantship by Government of India and Chemical Engineering Department, IIT, Roorkee for the facility provided for conducting research work. References [1] H. Song, Y. Liu, W. Xu, G. Zeng, N. Aibibu, L. Xu, B. Chen, Simultaneous Cr(VI) reduction and phenol degradation in pure cultures of Pseudomonas aeruginosa CCTCC AB91095, Bioresour.Technol. 100 (2009) 5079–5084.

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