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Thermodynamic, equilibrium and kinetic studies on biosorption of Pb+2 from aqueous solution by Bacillus pumilus sp. AS1 isolated from soil at abandoned lead mine
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Thermodynamic, equilibrium and kinetic studies on biosorption of Pb+2 from aqueous solution by Bacillus pumilus sp. AS1 isolated from soil at abandoned lead mine Shayan Sayyadi, Salman Ahmady-Asbchin∗, Kasra Kamali, Nadia Tavakoli Department of Cell and Molecular Biology, Faculty of Basic Sciences, University of Mazandaran, Babolsar, Mazandaran, Iran
a r t i c l e
i n f o
a b s t r a c t In this study, a lead-resistant bacterium was isolated and used as an adsorbent to remove Pb+2 from aqueous solution. The strain was identified and designated as Bacillus pumilus sp. AS1 based on the morphology and 16S rRNA sequence analysis. Biosorption of Pb+2 from aqueous solutions using AS1 was investigated under various experimental conditions of pH, initial metal concentration, contact time and temperature. The optimum pH value was determined to be 4.0. Pseudo-second-order kinetic model was also found to be in good agreement with the experimental results. Thermodynamic parameters of the adsorption confirmed the endothermic nature of sorption process with positive heat of enthalpy, accompanied by a positive value of entropy change. The results of FTIR analysis suggested the involvement of carboxyl and hydroxyl groups during the biosorption process. Scanning electron microscopy and energy dispersive X-ray spectroscopy analyses showed that biosorption of B. pumilus sp. AS1 to Pb+2 involved surface adsorption and ion exchange. Desorption experiments by treating biomass with 0.1 M HNO3 solution resulted to more than 90% recovery of the adsorbed Pb+2 from AS1, thereby indicating that Pb+2 can be easily and quantitatively recovered from biomass. © 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Article history: Received 23 April 2017 Revised 5 September 2017 Accepted 5 September 2017 Available online xxx Keywords: Lead Bioremediation Adsorption Bacteria 16S rRNA sequence analysis
1. Introduction Nowadays, heavy metal pollution has become a serious environmental problem due to the toxicity of these substances, the difficulty in their remediation [1] and their accumulation and maintenance in human body [2]. Therefore, it is necessary to treat metal-contaminated effluent before its discharge to the environment. From the heavy metals category, lead is one of the most toxic and noxious metals that contaminates the general environment through mining and smelting activities, combustion of leaded gasoline, land application of sewage sludge, disposal of batteries, printing and glass manufacturing [3,4]. In human, exposure to lead may cause many diseases like hepatitis, encephalopathy [5], intellectual disability, semi-permanent brain damage in young children [6] and it can also disturb hemoglobin synthesis [7]. Based on environmental problems caused by heavy metals and their harm on human, several conventional methods have been applied to remove heavy metals from metal contaminant effluent,
∗
Corresponding author. E-mail addresses: [email protected], Asbchin).
[email protected]
(S.
Ahmady-
such as filtration, flocculation, using activated charcoal, ion exchange resins, chemical precipitation, reverse osmosis and evaporation [8]. However, recently a new method which is called biosorption (a process in which some microorganisms such as bacteria, fungi, and algae are used to remove heavy metals from contaminated environments) has been demonstrated as an alternative to previous methods due to its potential to provide an effective and economic means for heavy metals remediation and it is also highly selective, easy to operate and cost effective in the treatment of large volumes of wastewater containing heavy metals. Besides, previous methods (e.g., ion exchange, flocculation) are incompetent, expensive and often cause a secondary problem like metal bearing sludge [9]. A lot of studies using different types of biomass have verified that biosorption is a more effective method for heavy metal removal in comparison with the conventional ones but further investigation is still needed in order to optimize the maximum efficiency of heavy-metal removal which inspires us to identify more strains that could be considered as biosorbent with high efficiency to remove heavy metals [10–12]. In the current work, Bacillus pumilus sp. AS1, isolated from industrial metal mine was examined to evaluate its ability for removing Pb+2 . Fourier transform infrared (FT-IR) analysis, scanning electron microscopy with energy dispersive X-ray (SEM/EDX) analysis,
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Please cite this article as: S. Sayyadi et al., Thermodynamic, equilibrium and kinetic studies on biosorption of Pb+2 from aqueous solution by Bacillus pumilus sp. AS1 isolated from soil at abandoned lead mine, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.09.005
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desorption efficiency of Pb+2 from loaded biosorbents and the influence of experimental parameters such as pH, contact time, temperature and initial lead concentration were studied as well. The kinetic and isotherm data of biosorption studies were processed to gain insight into the biosorption mechanism of the Pb+2 ions onto this bacterium. Therefore, the innovative aspect of this study was to introduce a new bacterium strain with the biosorption capacity for Pb+2 from aqueous solutions and lead us to a better understanding of biosorption phenomena.
2.4.2. Analysis of FT-IR Possible involvement of surface functional groups of bacterium during the removal of Pb+2 from aqueous solution was clarified using the Fourier transform infrared (FTIR) analysis. Overnight dried bacterial cell pellets were ground with KBr at a ratio of 1:200 in a mortar before pressed into 10 mm diameter disks under 6 tons of pressure for analysis [15].
2. Materials and methods
Errors might happen while biosorption experiments are conducted due to cross-contamination from used chemicals or glassware which results in the loss of ions in metal because of absorption or volatilization. The process of acidification of pH 1 and 2 has been carried out to bring about the reduction in and prevention of the aforementioned errors, through which the metabolism caused by microorganisms and hydrolysis and precipitation would be stopped. Moreover, to reduce bacterial activity cooling and freezing and water samples were stored in darkness and kept refrigerated (−4 °C) until the accomplishment of analysis process. Also, the reliability of analytical results would be enhanced by the shortest time between the sampling and the analysis. Until analyzing their metal content, the solutions of metal to have been stored in polyethylene bottles throughout this investigation. In order to diminish the loss of metal ions on the surface of polyethylene or Teflon bottles they are used in process of inorganic analysis. Moreover, metal solution samples have been acidified down to pH ∼ 2 (with HNO3 ) till analyses. It has been recommended to acidify the sample down to pH ∼ 2 in order to avoid adsorption on plastic bottles and hinders metal adsorption or precipitation of metal hydroxides ions which are piled up on the walls of the bottle. For example while cleaning glassware and plastic bottles with detergent they should be overnight immersed in 10% HNO3 beside rinsed with double distilled water (DDW) for several times. For blanks samples belonging to metal solutions have been employed without biosorbent to determine and come up with the initial metal concentration. It is of high importance that all experiments and measurements must be replicable in nature that means they are to be conducted in duplicates or triplicates [16].
2.1. Isolation and cultivation A bacterium strain capable of lead biosorption was isolated from soils from an abandoned metal mine sites in Zanjan, Iran (288,359.8300N; 4,055,475.77E). The strain was specified as Bacillus pumilus sp. AS1 based on sequence homology analysis of 16S rRNA gene as well as its physiological and biochemical properties. The 16S rRNA gene sequence has been deposited in GenBank (accession no. KY037799). Bacteria were cultured in Luria Bertani (LB) liquid medium, consisting of NaCl (10 g/L), tryptone (10 g/L) and yeast extract (5 g/L), pH 7.0, at 37 °C with shaking at 150 rpm for 24 h [13]. 2.2. Preparation of Pb+2 stock solutions Heavy metal stock solution was prepared as Pb (NO3 )2 (Merck KGaA, Darmstadt, Germany). The Pb+2 stock solution (10 0 0 mg/L) was prepared by dissolving the exact quantities of analytical grade Pb(NO3 )2 in Milli-Q water and filtering through a 0.22 mm filter (Pall Co., MI, USA). Working concentrations of Pb+2 were obtained by serial dilution and measured by flame atomic adsorption spectrometer (novAA 400p analytik Jena). The stock solutions were stored in the dark at 4 °C. 2.3. Batch biosorption experiments In order to study the effect of pH, equilibrium adsorption isotherm and adsorption kinetics on the Pb+2 adsorption process, batch biosorption studies were performed using 25 mL of Pb+2 solution and bacillus biomass (1 g/L) in different 100-mL Erlenmeyer flasks and incubated with shaking (150 rpm) at 30 °C for 60 min (except for the contact time experiment which varied from (0–180) min) unless stated otherwise. The desired pH values were achieved by adding small volumes of 0.1 mol/L HCl, or 0.1 mol/L NaOH solutions. The effect of pH on the biosorption capacity of the biomass was investigated by balancing the biosorbent and Pb+2 solutions at different pH values between 2 and 6. The contact time varied from (0 to 180) min for describing biosorption kinetics. The temperature effect was investigated at three temperatures of 10, 22 and 37 °C. Initial Pb+2 ion concentration was ranged from 25 to 300 mg/L in order to evaluate the equilibrium data for isotherm modeling. For recyclability testing, metal was eluted from the adsorption biomass with 0.1 M HNO3 , washed with deionized water, and used again for adsorption study. All the experiments were performed in triplicate, making an experimental error of less than 5% [14]. 2.4. Characterization of Pb+2 adsorption onto AS1 2.4.1. Analysis of SEM-EDX In order to study the surface morphology and elemental composition, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) was used before and after contacting with Pb+2 ions.
2.5. Quality control and quality assurance
3. Results and discussion 3.1. 16S rRNA gene sequence and phylogenetic analysis Gene sequence of the 16S rRNA gene containing 1354 nucleotides was determined for isolate AS1. Result of BLAST in EzTaxon database showed that the isolate AS1 98.8% similarity to B. pumilus. Based on the molecular analysis data, a phylogenetic tree was constructed by comparing nucleotide sequences with available 16S rRNA sequences. The bacterium isolate was identified as Bacillus pumilus sp. AS1. Constructed phylogenic tree was presented in Fig. 1. 3.2. Effect of initial pH Recent researchers have authentically emphasized on an undeniable fact which demonstrates that one of the most important factors that affect biosorption of metal ions is the acidity of solution. This parameter (pH) directly related with the competition ability of hydrogen ions with metal ions to active sites on the biosorbents surface. As shown in Fig. 2, biosorption rate is low at low pH (2); it can be explained regarding the fact that biosorbent structure is damaged by low initial pH of the solution. There is also an ionexchange competition between mobile H+ ions and Pb+2 ions to bind with functional groups on the biosorbent that creates a positive charge on the cell wall that leads to bringing up a repulsive
Please cite this article as: S. Sayyadi et al., Thermodynamic, equilibrium and kinetic studies on biosorption of Pb+2 from aqueous solution by Bacillus pumilus sp. AS1 isolated from soil at abandoned lead mine, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.09.005
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Fig. 1. Phylogenetic tree, based on 16S rRNA gene sequences accessible from the NCBI database (accession numbers are given in parentheses), drawn after several alignment of the data by ClustalX2. Clustering and distances were obtained using the software package MEGA 6 with the maximum likelihood method [28]. Bootstrap values based on 10 0 0 replications are listed as percentages at branching points. Bar, genetic distance of 0.01.
Fig. 2. Effect of pH on adsorption of Pb+2 by Bacillus pumilus sp. AS1 (metal concentration: 50 mg/L; temperature: 30 °C; biomass dosage: 1 g/L; contact time: 60 min).
force against heavy metal cations in the solution. Metal uptake by the biomass was increased with increasing pH and reached a maximum value after which it began to decrease since after pH 6, Pb(OH)+ and Pb(OH)2 become main dominant species in the solution [17,18]. As it can be seen from Fig. 2, the Pb+2 uptake Qe is almost constant between pH 3 and pH 6 but the biosorption rate at low pH (like pH 2) or high pH (like pH 9) has been noticeably affected. The optimum pH for Pb+2 turned out to be 4.0. Therefore, pH 4.0 was selected for all further studies. 3.3. Kinetic study One of the most important studies that must be taken into consideration is kinetic study that gives an insight into the rate as
Fig. 3. Effect of contact time on adsorption of Pb+2 by Bacillus pumilus sp. AS1 (metal concentration: 50 mg/L; temperature: 30 °C; biomass dosage: 1 g/L; pH: 4.0).
well as mechanism of the adsorption process. As can be seen in Fig. 3, the Pb+2 adsorption remarkably affected by the contact time. It can be observed that Pb+2 ions adsorption quickly increased at the beginning of biosorption, the maximum level of Pb+2 adsorption takes place in the first 20 min and thereafter gently reaches the dynamic equilibrium. After equilibrium (45 min) was reached, there was no significant change in adsorption. The reason that at the initial stage, adsorption was very fast may be attributed to the plenty of binding sites on the surface of the biomass, which became occupied and then decreased in adsorption
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Table 1 Parameters of isotherm model for Pb+2 calculated from the sorption data of Pb2+ on Bacillus pumilus sp. AS1.
1.8 1.6
Ions
qm (mmol/g)
bL (L/mmol)
R2
1.4
Pb+2
0.645
27.74
0.997
t/qt
1.2
y = 0.007x + 0.0584 R² = 0.9992
1 0.8
60 50
0.4 0.2 0 0
50
100
150 200 Time(min)
250
300
1/qe (g/mmol)
0.6
y = 43.37x + 1.5571 R² = 0.9974
40 30 20 10
Fig. 4. Pseudo-second-order rate kinetic of Pb+2 by Bacillus pumilus sp. AS1.
0 rate was observed. This time for maximum adsorption was selected as the optimum contact time for further experiments. In order to clarify the adsorption kinetic of Pb+2 onto Bacillus pumilus sp. AS1 biomass, two kinetic models, Lagergren’s pseudofirst-order (Eq. (1)) and pseudo-second-order (Eq. (2)) model, were applied to the experimental data.
ln(qe − qt ) = K1 t + ln qe
(1)
t 1 t = + qt qe K2 q2e
(2)
where qe and qt (mg/g) were the amounts of the metal ions biosorbed at equilibrium and t (min), respectively, while K1 and K2 being the rate constants of the first and second order rate equations (g/mg min), respectively. The biosorption rate constants K1 and K2 could be determined experimentally by plotting of ln(qe − qt ) vs t and t/qt vs t, respectively. Fig. 4 showed that the pseudo-second-order rate kinetics fit reasonably well (R2 > 0.999), which supported the experimental data for Pb+2 [19,20]. Generally, adsorption is a complex multistep process and kinetic studies will provide valuable insights of this process which involves mass transfer, diffusion and surface reaction phenomenon. The Lagergren’s rate equation is one of the most widely used rate equations to describe the adsorption of an adsorbate from the liquid phase. In this study the reaction fits well to pseudo second
0
0.2
0.4 0.6 1/Ce (L/mmol)
0.8
1
1.2
Fig. 6. Sorption isotherm of Pb+2 on the Bacillus pumilus sp. AS1 biomass in deionized water by Langmuir linear form.
order model that indicates an inclination toward chemisorption involving valence forces through the exchange of electrons between sorbent and sorbate. 3.4. Adsorption isotherm The adsorption isotherm of Pb+2 takes place in pH 4 and the obtained results are clearly shown in Fig. 5. While the concentration of Pb+2 increases, an increase in adsorption is observed as well. While this increase reaches the level at which the binding sites of AS1 fully loaded, no more adsorption increase would be observed by increasing metal concentrations [21]. The maximum level of adsorption through AS1 in Pb+2 is 0.671. To understand the adsorption process, the equilibrium adsorption data correlate to Langmuir linear equation (Eq. (3)) and obtained results are shown in Table 1 and Fig. 6 [22].
1 1 1 = + qe bqmCe qm
(3)
0.8 0.7
q e (mmol/g)
0.6 0.5 0.4 0.3 0.2 0.1 0 -50
-0.1 0
50
100
150
200
250
300
inial concentraon( mg/l) Fig. 5. Adsorption isotherm of Pb+2 on the Bacillus pumilus sp. AS1 biomass with different metal ion concentration.
Please cite this article as: S. Sayyadi et al., Thermodynamic, equilibrium and kinetic studies on biosorption of Pb+2 from aqueous solution by Bacillus pumilus sp. AS1 isolated from soil at abandoned lead mine, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.09.005
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Table 2 Values of ࢞H°, ࢞S° and ࢞G° calculated from the sorption data of Pb2+ on Bacillus pumilus sp. AS1. Sample
Pb
+2
-AS1
࢞H°(kJ/mol)
7.53
࢞S° (kJ/mol K)
0.027
࢞G°(kJ/mol) 283 K
298 K
313 K
−0.118
−0.561
−0.931
Table 3 Comparison of different bacterial biosorbents (growing in heavy metal contaminated sites) for Pb2+ removal. Metal Pb
Fig. 7. Plot of ࢞G vs T for the estimation of thermodynamic parameter for biosorption of Pb+2 onto Bacillus pumilus sp. AS1 biomass.
where qe is the equilibrium metal ion concentration on the adsorbent (mg/g), Ce is the equilibrium metal ion concentration in the solution (mg/L), qm is the maximum adsorption capacity of the biosorbents (mg/g), bL is the adsorption equilibrium constant. In this study, r2 for Pb+2 biosorption is 0.997 and bL is 27.74 (L/mmol). Adsorption isotherm of Pb+2 has followed Langmuir equation. Regarding the fact that adsorption isotherm of Pb+2 has followed Langmuir equation, it can be concluded that adsorption
+2
Biomass type
Metal uptake (mmol/g)
Ref.
Delftia tsuruhatensis Bacillus cereus 12-2 Bacillus cereus Alcaligenes sp. BAPb.1 Bacillus pumilus sp. AS1
0.216 1.642 0.579 0.322 0.645
[29] [13] [30] [31] Present study
occurs on a homogenous surface by monolayer sorption. In other words the Langmuir isotherm assumes monolayer adsorption onto a surface containing a finite number of adsorption sites of uniform strategies with no transmigration of adsorbate in the plane surface. Once a site is filled, no further sorption can take place at that site. This indicates that the surface reaches a saturation point where the maximum adsorption of the surface will be achieved. Zhang et al. [23] reported that Pb-tolerant strains are much more prevalent in soils with than without Pb. The results from our study support the hypothesis and Table 3 aims to contribute to a better understanding of the hypothesis. 3.5. Temperature effect In order to describe thermodynamic behavior of the biosorption of Pb+2 ions onto Bacillus pumilus sp. AS1 biomass, thermodynamic
Fig. 8. FTIR Spectrum of the Bacillus pumilus sp. AS1. (Before (1) and after (2) biosorption of Pb).
Please cite this article as: S. Sayyadi et al., Thermodynamic, equilibrium and kinetic studies on biosorption of Pb+2 from aqueous solution by Bacillus pumilus sp. AS1 isolated from soil at abandoned lead mine, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.09.005
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Fig. 9. SEM-EDX images of Bacillus pumilus sp. AS1 before and after contacting with Pb+2 : (1 and 2) before contacting; (3 and 4) after contacting.
parameters such as the change in free energy (࢞G°), enthalpy (࢞H°) and entropy (࢞S°) were estimated from change of equilibrium constants with temperature. The biosorption process of Pb+2 ions can be summarized by the following reversible process (4), which represents a heterogeneous equilibrium:
Pb+2 (solution )+biosorbent ↔ Pb+2 − biosorbent
(4)
The equilibrium constant of biosorption is defined as:
KC = Cad, eq /Ceq
and 4.2, respectively. The free energy of the adsorption is given by the following equation (Eq. (6)):
G◦ = −RT ln KC
G ◦ = H ◦ − T S ◦ (5)
where Cad , eq (mg/L) is the amount of Pb+2 ion biosorbed at equilibrium and Ceq (mg/L) is the Pb+2 ion concentration remaining in solution at equilibrium conditions. The Cad , eq value was determined as the difference of initial and remaining Pb+2 concentration in solution at equilibrium conditions. For the biosorption of Pb+2 ions on AS1, the KC values at 10, 20 and 40 °C were 2.9, 3.1,
(6)
where ࢞G° is standard free energy change (kJ/mol), R is the universal gas constant, and T is the absolute temperature (K). The Gibbs free energy can be represented as follows:
(7)
According to Eq. (7), Gibbs free energy change (࢞G°) was calculated to be −0.118, −0.561 and −0.931 kJ/mol for the biosorption of Pb+2 at 10, 20 and 40 °C, respectively. As shown in Fig. 7 and Table 2, the negative values of ࢞G° confirm the feasibility of the process and the spontaneous nature of biosorption with a high preference of Pb+2 on AS1. The increase of the absolute value of ࢞G° as temperatures rise indicates that the
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3.8. Desorption efficiency
Fig. 10. Desorption efficiency of Bacillus pumilus sp. AS1 biomass with cycle number. Data represent an average of three independent experiments, ±SD shown by error bar.
affinity of Pb+2 on AS1 was higher at high temperature. The positive value of ࢞H° suggests the endothermic nature of Pb+2 biosorption. The positive value of ࢞S° reveals the increased randomness at the solid–solution interface during the binding of the lead ion on the active sites of the biosorbent. Since the adsorption process is endothermic, it follows that under these conditions the process becomes spontaneous because of the positive entropy change [24].
3.6. FT-IR analysis In order to characterize the functional groups in the biosorbent, FTIR spectrum for the metal-loaded and metal-free biomass in the range of 60 0–380 0 cm−1 have been shown in Fig. 8. The FT-IR spectrum displays a number of absorption peaks, reflecting a complex nature of Bacillus pumilus sp. AS1 cell surfaces. FT-IR spectrum of AS1 in the absence and presence of Pb+2 revealed the changes in the peaks of functional groups, such as shifts 3425–3420 cm−1 indicating –OH stretching vibration after contacting with Pb+2 ; the peak at 1063 cm−1 shifted to 988 cm−1 after Pb+2 adsorption could be assigned to the stretching of C–O (carboxyl in the aromatic ring of AS1). The overall FT-IR spectra analysis implied that the functional groups like hydroxyl and carboxyl may be involved in Pb+2 adsorption and the results were in good agreement with those obtained by other researchers [25,26].
3.7. SEM-EDX analysis Further characterization of the adsorption process was done by energy dispersive X-ray (EDX) analysis which is one of the useful tools to evaluate the chemical and elemental analysis of biosorbents. Fig. 9 shows the typical EDX pattern for Bacillus pumilus sp. AS1, before and after the sorption of Pb+2 . The EDX pattern (Fig. 9(a) and (b)) for the unloaded (native) AS1 did not show the characteristic signal of Pb+2 , whereas for the Pb+2 -loaded MPW (Fig. 9(c) and (d)) a clear signal of the presence of Pb+2 was observed. Note that most biosorption studies determined metal sorption by measuring the residual metal concentrations in the supernatant, but did not directly prove the presence of the metals on the biomass. The results showed C (42.90%), O (41.90%), Ca (0.54%), K (0.17%), Cl (0.43%), N (12.11%) and P (0.77%) in the sample which was likely present in polysaccharides and proteins on the cell wall of the biomass.
The ability to regenerate the biomass is one of the most important aspects of biosorption. In order to show the reusability of the biosorbent, adsorption–desorption cycle of Pb+2 was repeated five times. As it can be seen from Fig. 10, the high stability of Bacillus pumilus sp. AS1 permitted five times of adsorption–elution process along the studies without a decrease about 10% in recovery of Pb+2 ions. Pb+2 ions adsorbed onto biosorbent were eluted with 0.1 M HNO3 . More than 90% of the adsorbed Pb+2 ions were desorbed from the biosorbents and the highest recovery values were obtained after the first cycle. As reported by Huang and Liu [15] the decrease in the adsorption capacities following desorption could be attributed to different reasons such as structural damage of biosorbent or blockage of binding sites by metal complex. These results showed that the biosorbent could be repeatedly used in Pb+2 ions adsorption studies without significant losses in its initial adsorption capacity. Similar observation was also reported in [27]. 4. Conclusions In this study, a lead-resistant bacterium strain was isolated and identified as Bacillus pumilus sp. AS1 based on the morphology and 16S rRNA sequence analysis that exhibited high biosorption rate and capacity for Pb+2 . FT-IR analyses indicated that hydroxyl and carboxyl may play vital roles in adsorption process. According to the parameters of the Langmuir isotherms, the maximum biosorption capacity of the biomass was found to be 0.671 mmol/g at optimum pH of 4. Pseudo-second-order kinetic model was also found to be in good agreement with the experimental results. The negative value of ࢞G° confirmed the spontaneous nature adsorption process. The positive value of ࢞S° showed the increased randomness at the solid–solution interface during adsorption and the positive value of ࢞H° indicated the adsorption process was endothermic. Desorption experiments showed that a reduction of biosorption capacity is noticed after the first cycle but the recovery of Pb+2 remained at high levels in all five cycles. Taken together, B. pumilus sp. AS1 could be seen as a microorganism capable of restoring polluted environments by lead which leads us to a conclusion in which bacteria that lived beside heavy metals have the ability to adsorb them. References [1] Puyen ZM, Villagrasa E, Maldonado J, Diestra E, Esteve I, Solé A. Biosorption of lead and copper by heavy-metal tolerant Micrococcus luteus DE2008. Bioresour Technol 2012;126:233–7. doi:10.1016/j.biortech.2012.09.036. [2] Reddy DHK, Seshaiah K, Reddy AVR, Rao MM, Wang MC. Biosorption of Pb2+ from aqueous solutions by Moringa oleifera bark: equilibrium and kinetic studies. J Hazard Mater 2010;174:831–8. doi:10.1016/j.jhazmat.2009.09.128. [3] Kang CH, Oh SJ, Shin Y, Han SH, Nam IH, So JS. Bioremediation of lead by ureolytic bacteria isolated from soil at abandoned metal mines in South Korea. Ecol Eng 2015;74:402–7. doi:10.1016/j.ecoleng.2014.10.009. [4] Morosanu I, Teodosiu C, Paduraru C, Ibanescu D, Tofan L. Biosorption of lead ions from aqueous effluents by rapeseed biomass. New Biotechnol 2016. doi:10.1016/j.nbt.2016.08.002. [5] Ren G, Jin Y, Zhang C, Gu H, Qu J. Characteristics of Bacillus sp. PZ-1 and its biosorption to Pb(II). Ecotoxicol Environ Saf 2015;117:141–8. doi:10.1016/j. ecoenv.2015.03.033. [6] Lawal OS, Sanni AR, Ajayi IA, Rabiu OO. Equilibrium, thermodynamic and kinetic studies for the biosorption of aqueous lead(II) ions onto the seed husk of Calophyllum inophyllum. J Hazard Mater 2010;177:829–35. doi:10.1016/ j.jhazmat.2009.12.108. [7] Halttunen T, Salminen S, Tahvonen R. Rapid removal of lead and cadmium from water by specific lactic acid bacteria. Int J Food Microbiol 2007;114:30–5. doi:10.1016/j.ijfoodmicro.2006.10.040. [8] Lakherwal D. Adsorption of heavy metals: a review. Int J Environ Res Dev 2014;4:41–8. [9] Lu WB, Shi JJ, Wang CH, Chang JS. Biosorption of lead, copper and cadmium by an indigenous isolate Enterobacter sp. J1 possessing high heavy-metal resistance. J Hazard Mater 2006;134:80–6. doi:10.1016/j.jhazmat.2005.10.036. [10] Yuan HP, Zhang JH, Lu ZM, Min H, Wu C. Studies on biosorption equilibrium and kinetics of Cd2+ by Streptomyces sp. K33 and HL-12. J Hazard Mater 2009;164:423–31. doi:10.1016/j.jhazmat.2008.08.014.
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[11] Rajasulochana P. Comparison on efficiency of various techniques in treatment of waste and sewage water – a comprehensive review. Resour Technol 2016;2:175–84. doi:10.1016/j.reffit.2016.09.004. [12] Veglio F, Beolchini F. Removal of metals by biosorption: a review. Hydrometallurgy 1997;44:301–16. [13] Chen Z, Pan X, Chen H, Guan X, Lin Z. Biomineralization of Pb(II) into Pbhydroxyapatite induced by Bacillus cereus 12-2 isolated from lead-zinc mine tailings. J Hazard Mater 2016;301:531–7. doi:10.1016/j.jhazmat.2015.09.023. [14] Tunali Akar S, Arslan D, Alp T. Ammonium pyrrolidine dithiocarbamate anchored Symphoricarpus albus biomass for lead(II) removal: batch and column biosorption study. J Hazard Mater 2012;227–228:107–17. doi:10.1016/j. jhazmat.2012.05.020. [15] Huang W, Liu ZM. Biosorption of Cd(II)/Pb(II) from aqueous solution by biosurfactant-producing bacteria: isotherm kinetic characteristic and mechanism studies. Colloids Surf B Biointerfaces 2013;105:113–19. doi:10.1016/j. colsurfb.2012.12.040. [16] Gupta VK, Rastogi A, Nayak A. Biosorption of nickel onto treated alga (Oedogonium hatei): application of isotherm and kinetic models. J Colloid Interface Sci 2010;342:533–9. doi:10.1016/j.jcis.2009.10.074. [17] Lü QF, Huang ZK, Liu B, Cheng X. Preparation and heavy metal ions biosorption of graft copolymers from enzymatic hydrolysis lignin and amino acids. Bioresour Technol 2012;104:111–18. doi:10.1016/j.biortech.2011.10.055. [18] Volesky B. Biosorption and me. Water Res 2007;41:4017–29. doi:10.1016/j. watres.2007.05.062. [19] Chen YG, Ye WM, Yang XM, Deng FY, He Y. Effect of contact time, pH, and ionic strength on Cd(II) adsorption from aqueous solution onto bentonite from Gaomiaozi, China. Environ Earth Sci 2011;64:329–36. doi:10.1007/ s12665- 010- 0850- 6. [20] Anayurt RA, Sari A, Tuzen M. Equilibrium, thermodynamic and kinetic studies on biosorption of Pb(II) and Cd(II) from aqueous solution by macrofungus (Lactarius scrobiculatus) biomass. Chem Eng J 2009;151:255–61. doi:10.1016/j. cej.20 09.03.0 02. [21] Markou G, Mitrogiannis D, Çelekli A, Bozkurt H, Georgakakis D, Chrysikopoulos CV. Biosorption of Cu2+ and Ni2+ by Arthrospira platensis with different biochemical compositions. Chem Eng J 2015;259:806–13. doi:10.1016/j.cej.2014. 08.037.
[22] Ebrahimi A, Ehteshami M, Dahrazma B. Isotherm and kinetic studies for the biosorption of cadmium from aqueous solution by Alhaji maurorum seed. Process Saf Environ Prot 2015;98:374–82. doi:10.1016/j.psep.2015.09.013. [23] Zhang H-B, Yang M-X, Shi W, Zheng Y, Sha T, Zhao Z-W. Bacterial diversity in mine tailings compared by cultivation and cultivation-independent methods and their resistance to lead and cadmium. Microb Ecol 2007;54:705–12. doi:10.10 07/s0 0248-0 07- 9229- y. [24] Tabaraki R, Nateghi A, Ahmady-Asbchin S. International biodeterioration & biodegradation biosorption of lead (II) ions on Sargassum ilicifolium: application of response surface methodology. Int Biodeterior Biodegradation 2014;93:145–52. doi:10.1016/j.ibiod.2014.03.022. [25] Tunali S, Çabuk A, Akar T. Removal of lead and copper ions from aqueous solutions by bacterial strain isolated from soil. Chem Eng J 2006;115:203–11. doi:10.1016/j.cej.2005.09.023. [26] Selatnia A, Boukazoula A, Kechid N, Bakhti MZ, Chergui A, Kerchich Y. Biosorption of lead (II) from aqueous solution by a bacterial dead Streptomyces rimosus biomass. Biochem Eng J 2004;19:127–35. doi:10.1016/j.bej.2003.12.007. [27] Gupta VK, Rastogi A. Sorption and desorption studies of chromium(VI) from nonviable cyanobacterium Nostoc muscorum biomass. J Hazard Mater 2008;154:347–54. doi:10.1016/j.jhazmat.2007.10.032. [28] Tamura K, Peterson D, Peterson N, Stecher G, Nei M, Kumar S. MEGA5: molecular evolutionary genetics analysis using maximum likelihood, evolutionary distance, and maximum parsimony methods. Mol Biol Evol 2011;28:2731–9. doi:10.1093/molbev/msr121. [29] Bautista-Hernández DA, Ramírez-Burgos LI, Duran-Páramo E, FernándezLinares L. Zinc and lead biosorption by Delftia tsuruhatensis: a bacterial strain resistant to metals isolated from mine tailings. J Water Resour Protect 2012;2012:207–16. [30] Murthy S, Bali G, Sarangi SK, Info P. Effect of lead on growth, protein and biosorption capacity of bacillus cereus isolated from industrial effluent. J Environ Biol 2014;35:407–11. [31] Jin Y, Yu S, Teng C, Song T, Dong L, Liang J, et al. Biosorption characteristic of Alcaligenes sp. BAPb.1 for removal of lead(II) from aqueous solution. 3 Biotech 2017;7:123. doi:10.1007/s13205- 017- 0721- x.
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Thermodynamic, equilibrium and kinetic studies on biosorption of Pb+2 from aqueous solution by Bacillus pumilus sp. AS1 isolated from soil at abandoned lead mine Shayan Sayyadi, Salman Ahmady-Asbchin∗, Kasra Kamali, Nadia Tavakoli Department of Cell and Molecular Biology, Faculty of Basic Sciences, University of Mazandaran, Babolsar, Mazandaran, Iran
a r t i c l e
i n f o
a b s t r a c t In this study, a lead-resistant bacterium was isolated and used as an adsorbent to remove Pb+2 from aqueous solution. The strain was identified and designated as Bacillus pumilus sp. AS1 based on the morphology and 16S rRNA sequence analysis. Biosorption of Pb+2 from aqueous solutions using AS1 was investigated under various experimental conditions of pH, initial metal concentration, contact time and temperature. The optimum pH value was determined to be 4.0. Pseudo-second-order kinetic model was also found to be in good agreement with the experimental results. Thermodynamic parameters of the adsorption confirmed the endothermic nature of sorption process with positive heat of enthalpy, accompanied by a positive value of entropy change. The results of FTIR analysis suggested the involvement of carboxyl and hydroxyl groups during the biosorption process. Scanning electron microscopy and energy dispersive X-ray spectroscopy analyses showed that biosorption of B. pumilus sp. AS1 to Pb+2 involved surface adsorption and ion exchange. Desorption experiments by treating biomass with 0.1 M HNO3 solution resulted to more than 90% recovery of the adsorbed Pb+2 from AS1, thereby indicating that Pb+2 can be easily and quantitatively recovered from biomass. © 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Article history: Received 23 April 2017 Revised 5 September 2017 Accepted 5 September 2017 Available online xxx Keywords: Lead Bioremediation Adsorption Bacteria 16S rRNA sequence analysis
1. Introduction Nowadays, heavy metal pollution has become a serious environmental problem due to the toxicity of these substances, the difficulty in their remediation [1] and their accumulation and maintenance in human body [2]. Therefore, it is necessary to treat metal-contaminated effluent before its discharge to the environment. From the heavy metals category, lead is one of the most toxic and noxious metals that contaminates the general environment through mining and smelting activities, combustion of leaded gasoline, land application of sewage sludge, disposal of batteries, printing and glass manufacturing [3,4]. In human, exposure to lead may cause many diseases like hepatitis, encephalopathy [5], intellectual disability, semi-permanent brain damage in young children [6] and it can also disturb hemoglobin synthesis [7]. Based on environmental problems caused by heavy metals and their harm on human, several conventional methods have been applied to remove heavy metals from metal contaminant effluent,
∗
Corresponding author. E-mail addresses: [email protected], Asbchin).
[email protected]
(S.
Ahmady-
such as filtration, flocculation, using activated charcoal, ion exchange resins, chemical precipitation, reverse osmosis and evaporation [8]. However, recently a new method which is called biosorption (a process in which some microorganisms such as bacteria, fungi, and algae are used to remove heavy metals from contaminated environments) has been demonstrated as an alternative to previous methods due to its potential to provide an effective and economic means for heavy metals remediation and it is also highly selective, easy to operate and cost effective in the treatment of large volumes of wastewater containing heavy metals. Besides, previous methods (e.g., ion exchange, flocculation) are incompetent, expensive and often cause a secondary problem like metal bearing sludge [9]. A lot of studies using different types of biomass have verified that biosorption is a more effective method for heavy metal removal in comparison with the conventional ones but further investigation is still needed in order to optimize the maximum efficiency of heavy-metal removal which inspires us to identify more strains that could be considered as biosorbent with high efficiency to remove heavy metals [10–12]. In the current work, Bacillus pumilus sp. AS1, isolated from industrial metal mine was examined to evaluate its ability for removing Pb+2 . Fourier transform infrared (FT-IR) analysis, scanning electron microscopy with energy dispersive X-ray (SEM/EDX) analysis,
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desorption efficiency of Pb+2 from loaded biosorbents and the influence of experimental parameters such as pH, contact time, temperature and initial lead concentration were studied as well. The kinetic and isotherm data of biosorption studies were processed to gain insight into the biosorption mechanism of the Pb+2 ions onto this bacterium. Therefore, the innovative aspect of this study was to introduce a new bacterium strain with the biosorption capacity for Pb+2 from aqueous solutions and lead us to a better understanding of biosorption phenomena.
2.4.2. Analysis of FT-IR Possible involvement of surface functional groups of bacterium during the removal of Pb+2 from aqueous solution was clarified using the Fourier transform infrared (FTIR) analysis. Overnight dried bacterial cell pellets were ground with KBr at a ratio of 1:200 in a mortar before pressed into 10 mm diameter disks under 6 tons of pressure for analysis [15].
2. Materials and methods
Errors might happen while biosorption experiments are conducted due to cross-contamination from used chemicals or glassware which results in the loss of ions in metal because of absorption or volatilization. The process of acidification of pH 1 and 2 has been carried out to bring about the reduction in and prevention of the aforementioned errors, through which the metabolism caused by microorganisms and hydrolysis and precipitation would be stopped. Moreover, to reduce bacterial activity cooling and freezing and water samples were stored in darkness and kept refrigerated (−4 °C) until the accomplishment of analysis process. Also, the reliability of analytical results would be enhanced by the shortest time between the sampling and the analysis. Until analyzing their metal content, the solutions of metal to have been stored in polyethylene bottles throughout this investigation. In order to diminish the loss of metal ions on the surface of polyethylene or Teflon bottles they are used in process of inorganic analysis. Moreover, metal solution samples have been acidified down to pH ∼ 2 (with HNO3 ) till analyses. It has been recommended to acidify the sample down to pH ∼ 2 in order to avoid adsorption on plastic bottles and hinders metal adsorption or precipitation of metal hydroxides ions which are piled up on the walls of the bottle. For example while cleaning glassware and plastic bottles with detergent they should be overnight immersed in 10% HNO3 beside rinsed with double distilled water (DDW) for several times. For blanks samples belonging to metal solutions have been employed without biosorbent to determine and come up with the initial metal concentration. It is of high importance that all experiments and measurements must be replicable in nature that means they are to be conducted in duplicates or triplicates [16].
2.1. Isolation and cultivation A bacterium strain capable of lead biosorption was isolated from soils from an abandoned metal mine sites in Zanjan, Iran (288,359.8300N; 4,055,475.77E). The strain was specified as Bacillus pumilus sp. AS1 based on sequence homology analysis of 16S rRNA gene as well as its physiological and biochemical properties. The 16S rRNA gene sequence has been deposited in GenBank (accession no. KY037799). Bacteria were cultured in Luria Bertani (LB) liquid medium, consisting of NaCl (10 g/L), tryptone (10 g/L) and yeast extract (5 g/L), pH 7.0, at 37 °C with shaking at 150 rpm for 24 h [13]. 2.2. Preparation of Pb+2 stock solutions Heavy metal stock solution was prepared as Pb (NO3 )2 (Merck KGaA, Darmstadt, Germany). The Pb+2 stock solution (10 0 0 mg/L) was prepared by dissolving the exact quantities of analytical grade Pb(NO3 )2 in Milli-Q water and filtering through a 0.22 mm filter (Pall Co., MI, USA). Working concentrations of Pb+2 were obtained by serial dilution and measured by flame atomic adsorption spectrometer (novAA 400p analytik Jena). The stock solutions were stored in the dark at 4 °C. 2.3. Batch biosorption experiments In order to study the effect of pH, equilibrium adsorption isotherm and adsorption kinetics on the Pb+2 adsorption process, batch biosorption studies were performed using 25 mL of Pb+2 solution and bacillus biomass (1 g/L) in different 100-mL Erlenmeyer flasks and incubated with shaking (150 rpm) at 30 °C for 60 min (except for the contact time experiment which varied from (0–180) min) unless stated otherwise. The desired pH values were achieved by adding small volumes of 0.1 mol/L HCl, or 0.1 mol/L NaOH solutions. The effect of pH on the biosorption capacity of the biomass was investigated by balancing the biosorbent and Pb+2 solutions at different pH values between 2 and 6. The contact time varied from (0 to 180) min for describing biosorption kinetics. The temperature effect was investigated at three temperatures of 10, 22 and 37 °C. Initial Pb+2 ion concentration was ranged from 25 to 300 mg/L in order to evaluate the equilibrium data for isotherm modeling. For recyclability testing, metal was eluted from the adsorption biomass with 0.1 M HNO3 , washed with deionized water, and used again for adsorption study. All the experiments were performed in triplicate, making an experimental error of less than 5% [14]. 2.4. Characterization of Pb+2 adsorption onto AS1 2.4.1. Analysis of SEM-EDX In order to study the surface morphology and elemental composition, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) was used before and after contacting with Pb+2 ions.
2.5. Quality control and quality assurance
3. Results and discussion 3.1. 16S rRNA gene sequence and phylogenetic analysis Gene sequence of the 16S rRNA gene containing 1354 nucleotides was determined for isolate AS1. Result of BLAST in EzTaxon database showed that the isolate AS1 98.8% similarity to B. pumilus. Based on the molecular analysis data, a phylogenetic tree was constructed by comparing nucleotide sequences with available 16S rRNA sequences. The bacterium isolate was identified as Bacillus pumilus sp. AS1. Constructed phylogenic tree was presented in Fig. 1. 3.2. Effect of initial pH Recent researchers have authentically emphasized on an undeniable fact which demonstrates that one of the most important factors that affect biosorption of metal ions is the acidity of solution. This parameter (pH) directly related with the competition ability of hydrogen ions with metal ions to active sites on the biosorbents surface. As shown in Fig. 2, biosorption rate is low at low pH (2); it can be explained regarding the fact that biosorbent structure is damaged by low initial pH of the solution. There is also an ionexchange competition between mobile H+ ions and Pb+2 ions to bind with functional groups on the biosorbent that creates a positive charge on the cell wall that leads to bringing up a repulsive
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Fig. 1. Phylogenetic tree, based on 16S rRNA gene sequences accessible from the NCBI database (accession numbers are given in parentheses), drawn after several alignment of the data by ClustalX2. Clustering and distances were obtained using the software package MEGA 6 with the maximum likelihood method [28]. Bootstrap values based on 10 0 0 replications are listed as percentages at branching points. Bar, genetic distance of 0.01.
Fig. 2. Effect of pH on adsorption of Pb+2 by Bacillus pumilus sp. AS1 (metal concentration: 50 mg/L; temperature: 30 °C; biomass dosage: 1 g/L; contact time: 60 min).
force against heavy metal cations in the solution. Metal uptake by the biomass was increased with increasing pH and reached a maximum value after which it began to decrease since after pH 6, Pb(OH)+ and Pb(OH)2 become main dominant species in the solution [17,18]. As it can be seen from Fig. 2, the Pb+2 uptake Qe is almost constant between pH 3 and pH 6 but the biosorption rate at low pH (like pH 2) or high pH (like pH 9) has been noticeably affected. The optimum pH for Pb+2 turned out to be 4.0. Therefore, pH 4.0 was selected for all further studies. 3.3. Kinetic study One of the most important studies that must be taken into consideration is kinetic study that gives an insight into the rate as
Fig. 3. Effect of contact time on adsorption of Pb+2 by Bacillus pumilus sp. AS1 (metal concentration: 50 mg/L; temperature: 30 °C; biomass dosage: 1 g/L; pH: 4.0).
well as mechanism of the adsorption process. As can be seen in Fig. 3, the Pb+2 adsorption remarkably affected by the contact time. It can be observed that Pb+2 ions adsorption quickly increased at the beginning of biosorption, the maximum level of Pb+2 adsorption takes place in the first 20 min and thereafter gently reaches the dynamic equilibrium. After equilibrium (45 min) was reached, there was no significant change in adsorption. The reason that at the initial stage, adsorption was very fast may be attributed to the plenty of binding sites on the surface of the biomass, which became occupied and then decreased in adsorption
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Table 1 Parameters of isotherm model for Pb+2 calculated from the sorption data of Pb2+ on Bacillus pumilus sp. AS1.
1.8 1.6
Ions
qm (mmol/g)
bL (L/mmol)
R2
1.4
Pb+2
0.645
27.74
0.997
t/qt
1.2
y = 0.007x + 0.0584 R² = 0.9992
1 0.8
60 50
0.4 0.2 0 0
50
100
150 200 Time(min)
250
300
1/qe (g/mmol)
0.6
y = 43.37x + 1.5571 R² = 0.9974
40 30 20 10
Fig. 4. Pseudo-second-order rate kinetic of Pb+2 by Bacillus pumilus sp. AS1.
0 rate was observed. This time for maximum adsorption was selected as the optimum contact time for further experiments. In order to clarify the adsorption kinetic of Pb+2 onto Bacillus pumilus sp. AS1 biomass, two kinetic models, Lagergren’s pseudofirst-order (Eq. (1)) and pseudo-second-order (Eq. (2)) model, were applied to the experimental data.
ln(qe − qt ) = K1 t + ln qe
(1)
t 1 t = + qt qe K2 q2e
(2)
where qe and qt (mg/g) were the amounts of the metal ions biosorbed at equilibrium and t (min), respectively, while K1 and K2 being the rate constants of the first and second order rate equations (g/mg min), respectively. The biosorption rate constants K1 and K2 could be determined experimentally by plotting of ln(qe − qt ) vs t and t/qt vs t, respectively. Fig. 4 showed that the pseudo-second-order rate kinetics fit reasonably well (R2 > 0.999), which supported the experimental data for Pb+2 [19,20]. Generally, adsorption is a complex multistep process and kinetic studies will provide valuable insights of this process which involves mass transfer, diffusion and surface reaction phenomenon. The Lagergren’s rate equation is one of the most widely used rate equations to describe the adsorption of an adsorbate from the liquid phase. In this study the reaction fits well to pseudo second
0
0.2
0.4 0.6 1/Ce (L/mmol)
0.8
1
1.2
Fig. 6. Sorption isotherm of Pb+2 on the Bacillus pumilus sp. AS1 biomass in deionized water by Langmuir linear form.
order model that indicates an inclination toward chemisorption involving valence forces through the exchange of electrons between sorbent and sorbate. 3.4. Adsorption isotherm The adsorption isotherm of Pb+2 takes place in pH 4 and the obtained results are clearly shown in Fig. 5. While the concentration of Pb+2 increases, an increase in adsorption is observed as well. While this increase reaches the level at which the binding sites of AS1 fully loaded, no more adsorption increase would be observed by increasing metal concentrations [21]. The maximum level of adsorption through AS1 in Pb+2 is 0.671. To understand the adsorption process, the equilibrium adsorption data correlate to Langmuir linear equation (Eq. (3)) and obtained results are shown in Table 1 and Fig. 6 [22].
1 1 1 = + qe bqmCe qm
(3)
0.8 0.7
q e (mmol/g)
0.6 0.5 0.4 0.3 0.2 0.1 0 -50
-0.1 0
50
100
150
200
250
300
inial concentraon( mg/l) Fig. 5. Adsorption isotherm of Pb+2 on the Bacillus pumilus sp. AS1 biomass with different metal ion concentration.
Please cite this article as: S. Sayyadi et al., Thermodynamic, equilibrium and kinetic studies on biosorption of Pb+2 from aqueous solution by Bacillus pumilus sp. AS1 isolated from soil at abandoned lead mine, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.09.005
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Table 2 Values of ࢞H°, ࢞S° and ࢞G° calculated from the sorption data of Pb2+ on Bacillus pumilus sp. AS1. Sample
Pb
+2
-AS1
࢞H°(kJ/mol)
7.53
࢞S° (kJ/mol K)
0.027
࢞G°(kJ/mol) 283 K
298 K
313 K
−0.118
−0.561
−0.931
Table 3 Comparison of different bacterial biosorbents (growing in heavy metal contaminated sites) for Pb2+ removal. Metal Pb
Fig. 7. Plot of ࢞G vs T for the estimation of thermodynamic parameter for biosorption of Pb+2 onto Bacillus pumilus sp. AS1 biomass.
where qe is the equilibrium metal ion concentration on the adsorbent (mg/g), Ce is the equilibrium metal ion concentration in the solution (mg/L), qm is the maximum adsorption capacity of the biosorbents (mg/g), bL is the adsorption equilibrium constant. In this study, r2 for Pb+2 biosorption is 0.997 and bL is 27.74 (L/mmol). Adsorption isotherm of Pb+2 has followed Langmuir equation. Regarding the fact that adsorption isotherm of Pb+2 has followed Langmuir equation, it can be concluded that adsorption
+2
Biomass type
Metal uptake (mmol/g)
Ref.
Delftia tsuruhatensis Bacillus cereus 12-2 Bacillus cereus Alcaligenes sp. BAPb.1 Bacillus pumilus sp. AS1
0.216 1.642 0.579 0.322 0.645
[29] [13] [30] [31] Present study
occurs on a homogenous surface by monolayer sorption. In other words the Langmuir isotherm assumes monolayer adsorption onto a surface containing a finite number of adsorption sites of uniform strategies with no transmigration of adsorbate in the plane surface. Once a site is filled, no further sorption can take place at that site. This indicates that the surface reaches a saturation point where the maximum adsorption of the surface will be achieved. Zhang et al. [23] reported that Pb-tolerant strains are much more prevalent in soils with than without Pb. The results from our study support the hypothesis and Table 3 aims to contribute to a better understanding of the hypothesis. 3.5. Temperature effect In order to describe thermodynamic behavior of the biosorption of Pb+2 ions onto Bacillus pumilus sp. AS1 biomass, thermodynamic
Fig. 8. FTIR Spectrum of the Bacillus pumilus sp. AS1. (Before (1) and after (2) biosorption of Pb).
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Fig. 9. SEM-EDX images of Bacillus pumilus sp. AS1 before and after contacting with Pb+2 : (1 and 2) before contacting; (3 and 4) after contacting.
parameters such as the change in free energy (࢞G°), enthalpy (࢞H°) and entropy (࢞S°) were estimated from change of equilibrium constants with temperature. The biosorption process of Pb+2 ions can be summarized by the following reversible process (4), which represents a heterogeneous equilibrium:
Pb+2 (solution )+biosorbent ↔ Pb+2 − biosorbent
(4)
The equilibrium constant of biosorption is defined as:
KC = Cad, eq /Ceq
and 4.2, respectively. The free energy of the adsorption is given by the following equation (Eq. (6)):
G◦ = −RT ln KC
G ◦ = H ◦ − T S ◦ (5)
where Cad , eq (mg/L) is the amount of Pb+2 ion biosorbed at equilibrium and Ceq (mg/L) is the Pb+2 ion concentration remaining in solution at equilibrium conditions. The Cad , eq value was determined as the difference of initial and remaining Pb+2 concentration in solution at equilibrium conditions. For the biosorption of Pb+2 ions on AS1, the KC values at 10, 20 and 40 °C were 2.9, 3.1,
(6)
where ࢞G° is standard free energy change (kJ/mol), R is the universal gas constant, and T is the absolute temperature (K). The Gibbs free energy can be represented as follows:
(7)
According to Eq. (7), Gibbs free energy change (࢞G°) was calculated to be −0.118, −0.561 and −0.931 kJ/mol for the biosorption of Pb+2 at 10, 20 and 40 °C, respectively. As shown in Fig. 7 and Table 2, the negative values of ࢞G° confirm the feasibility of the process and the spontaneous nature of biosorption with a high preference of Pb+2 on AS1. The increase of the absolute value of ࢞G° as temperatures rise indicates that the
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3.8. Desorption efficiency
Fig. 10. Desorption efficiency of Bacillus pumilus sp. AS1 biomass with cycle number. Data represent an average of three independent experiments, ±SD shown by error bar.
affinity of Pb+2 on AS1 was higher at high temperature. The positive value of ࢞H° suggests the endothermic nature of Pb+2 biosorption. The positive value of ࢞S° reveals the increased randomness at the solid–solution interface during the binding of the lead ion on the active sites of the biosorbent. Since the adsorption process is endothermic, it follows that under these conditions the process becomes spontaneous because of the positive entropy change [24].
3.6. FT-IR analysis In order to characterize the functional groups in the biosorbent, FTIR spectrum for the metal-loaded and metal-free biomass in the range of 60 0–380 0 cm−1 have been shown in Fig. 8. The FT-IR spectrum displays a number of absorption peaks, reflecting a complex nature of Bacillus pumilus sp. AS1 cell surfaces. FT-IR spectrum of AS1 in the absence and presence of Pb+2 revealed the changes in the peaks of functional groups, such as shifts 3425–3420 cm−1 indicating –OH stretching vibration after contacting with Pb+2 ; the peak at 1063 cm−1 shifted to 988 cm−1 after Pb+2 adsorption could be assigned to the stretching of C–O (carboxyl in the aromatic ring of AS1). The overall FT-IR spectra analysis implied that the functional groups like hydroxyl and carboxyl may be involved in Pb+2 adsorption and the results were in good agreement with those obtained by other researchers [25,26].
3.7. SEM-EDX analysis Further characterization of the adsorption process was done by energy dispersive X-ray (EDX) analysis which is one of the useful tools to evaluate the chemical and elemental analysis of biosorbents. Fig. 9 shows the typical EDX pattern for Bacillus pumilus sp. AS1, before and after the sorption of Pb+2 . The EDX pattern (Fig. 9(a) and (b)) for the unloaded (native) AS1 did not show the characteristic signal of Pb+2 , whereas for the Pb+2 -loaded MPW (Fig. 9(c) and (d)) a clear signal of the presence of Pb+2 was observed. Note that most biosorption studies determined metal sorption by measuring the residual metal concentrations in the supernatant, but did not directly prove the presence of the metals on the biomass. The results showed C (42.90%), O (41.90%), Ca (0.54%), K (0.17%), Cl (0.43%), N (12.11%) and P (0.77%) in the sample which was likely present in polysaccharides and proteins on the cell wall of the biomass.
The ability to regenerate the biomass is one of the most important aspects of biosorption. In order to show the reusability of the biosorbent, adsorption–desorption cycle of Pb+2 was repeated five times. As it can be seen from Fig. 10, the high stability of Bacillus pumilus sp. AS1 permitted five times of adsorption–elution process along the studies without a decrease about 10% in recovery of Pb+2 ions. Pb+2 ions adsorbed onto biosorbent were eluted with 0.1 M HNO3 . More than 90% of the adsorbed Pb+2 ions were desorbed from the biosorbents and the highest recovery values were obtained after the first cycle. As reported by Huang and Liu [15] the decrease in the adsorption capacities following desorption could be attributed to different reasons such as structural damage of biosorbent or blockage of binding sites by metal complex. These results showed that the biosorbent could be repeatedly used in Pb+2 ions adsorption studies without significant losses in its initial adsorption capacity. Similar observation was also reported in [27]. 4. Conclusions In this study, a lead-resistant bacterium strain was isolated and identified as Bacillus pumilus sp. AS1 based on the morphology and 16S rRNA sequence analysis that exhibited high biosorption rate and capacity for Pb+2 . FT-IR analyses indicated that hydroxyl and carboxyl may play vital roles in adsorption process. According to the parameters of the Langmuir isotherms, the maximum biosorption capacity of the biomass was found to be 0.671 mmol/g at optimum pH of 4. Pseudo-second-order kinetic model was also found to be in good agreement with the experimental results. The negative value of ࢞G° confirmed the spontaneous nature adsorption process. The positive value of ࢞S° showed the increased randomness at the solid–solution interface during adsorption and the positive value of ࢞H° indicated the adsorption process was endothermic. Desorption experiments showed that a reduction of biosorption capacity is noticed after the first cycle but the recovery of Pb+2 remained at high levels in all five cycles. Taken together, B. pumilus sp. AS1 could be seen as a microorganism capable of restoring polluted environments by lead which leads us to a conclusion in which bacteria that lived beside heavy metals have the ability to adsorb them. References [1] Puyen ZM, Villagrasa E, Maldonado J, Diestra E, Esteve I, Solé A. Biosorption of lead and copper by heavy-metal tolerant Micrococcus luteus DE2008. Bioresour Technol 2012;126:233–7. doi:10.1016/j.biortech.2012.09.036. [2] Reddy DHK, Seshaiah K, Reddy AVR, Rao MM, Wang MC. Biosorption of Pb2+ from aqueous solutions by Moringa oleifera bark: equilibrium and kinetic studies. J Hazard Mater 2010;174:831–8. doi:10.1016/j.jhazmat.2009.09.128. [3] Kang CH, Oh SJ, Shin Y, Han SH, Nam IH, So JS. Bioremediation of lead by ureolytic bacteria isolated from soil at abandoned metal mines in South Korea. Ecol Eng 2015;74:402–7. doi:10.1016/j.ecoleng.2014.10.009. [4] Morosanu I, Teodosiu C, Paduraru C, Ibanescu D, Tofan L. Biosorption of lead ions from aqueous effluents by rapeseed biomass. New Biotechnol 2016. doi:10.1016/j.nbt.2016.08.002. [5] Ren G, Jin Y, Zhang C, Gu H, Qu J. Characteristics of Bacillus sp. PZ-1 and its biosorption to Pb(II). Ecotoxicol Environ Saf 2015;117:141–8. doi:10.1016/j. ecoenv.2015.03.033. [6] Lawal OS, Sanni AR, Ajayi IA, Rabiu OO. Equilibrium, thermodynamic and kinetic studies for the biosorption of aqueous lead(II) ions onto the seed husk of Calophyllum inophyllum. J Hazard Mater 2010;177:829–35. doi:10.1016/ j.jhazmat.2009.12.108. [7] Halttunen T, Salminen S, Tahvonen R. Rapid removal of lead and cadmium from water by specific lactic acid bacteria. Int J Food Microbiol 2007;114:30–5. doi:10.1016/j.ijfoodmicro.2006.10.040. [8] Lakherwal D. Adsorption of heavy metals: a review. Int J Environ Res Dev 2014;4:41–8. [9] Lu WB, Shi JJ, Wang CH, Chang JS. Biosorption of lead, copper and cadmium by an indigenous isolate Enterobacter sp. J1 possessing high heavy-metal resistance. J Hazard Mater 2006;134:80–6. doi:10.1016/j.jhazmat.2005.10.036. [10] Yuan HP, Zhang JH, Lu ZM, Min H, Wu C. Studies on biosorption equilibrium and kinetics of Cd2+ by Streptomyces sp. K33 and HL-12. J Hazard Mater 2009;164:423–31. doi:10.1016/j.jhazmat.2008.08.014.
Please cite this article as: S. Sayyadi et al., Thermodynamic, equilibrium and kinetic studies on biosorption of Pb+2 from aqueous solution by Bacillus pumilus sp. AS1 isolated from soil at abandoned lead mine, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.09.005
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[11] Rajasulochana P. Comparison on efficiency of various techniques in treatment of waste and sewage water – a comprehensive review. Resour Technol 2016;2:175–84. doi:10.1016/j.reffit.2016.09.004. [12] Veglio F, Beolchini F. Removal of metals by biosorption: a review. Hydrometallurgy 1997;44:301–16. [13] Chen Z, Pan X, Chen H, Guan X, Lin Z. Biomineralization of Pb(II) into Pbhydroxyapatite induced by Bacillus cereus 12-2 isolated from lead-zinc mine tailings. J Hazard Mater 2016;301:531–7. doi:10.1016/j.jhazmat.2015.09.023. [14] Tunali Akar S, Arslan D, Alp T. Ammonium pyrrolidine dithiocarbamate anchored Symphoricarpus albus biomass for lead(II) removal: batch and column biosorption study. J Hazard Mater 2012;227–228:107–17. doi:10.1016/j. jhazmat.2012.05.020. [15] Huang W, Liu ZM. Biosorption of Cd(II)/Pb(II) from aqueous solution by biosurfactant-producing bacteria: isotherm kinetic characteristic and mechanism studies. Colloids Surf B Biointerfaces 2013;105:113–19. doi:10.1016/j. colsurfb.2012.12.040. [16] Gupta VK, Rastogi A, Nayak A. Biosorption of nickel onto treated alga (Oedogonium hatei): application of isotherm and kinetic models. J Colloid Interface Sci 2010;342:533–9. doi:10.1016/j.jcis.2009.10.074. [17] Lü QF, Huang ZK, Liu B, Cheng X. Preparation and heavy metal ions biosorption of graft copolymers from enzymatic hydrolysis lignin and amino acids. Bioresour Technol 2012;104:111–18. doi:10.1016/j.biortech.2011.10.055. [18] Volesky B. Biosorption and me. Water Res 2007;41:4017–29. doi:10.1016/j. watres.2007.05.062. [19] Chen YG, Ye WM, Yang XM, Deng FY, He Y. Effect of contact time, pH, and ionic strength on Cd(II) adsorption from aqueous solution onto bentonite from Gaomiaozi, China. Environ Earth Sci 2011;64:329–36. doi:10.1007/ s12665- 010- 0850- 6. [20] Anayurt RA, Sari A, Tuzen M. Equilibrium, thermodynamic and kinetic studies on biosorption of Pb(II) and Cd(II) from aqueous solution by macrofungus (Lactarius scrobiculatus) biomass. Chem Eng J 2009;151:255–61. doi:10.1016/j. cej.20 09.03.0 02. [21] Markou G, Mitrogiannis D, Çelekli A, Bozkurt H, Georgakakis D, Chrysikopoulos CV. Biosorption of Cu2+ and Ni2+ by Arthrospira platensis with different biochemical compositions. Chem Eng J 2015;259:806–13. doi:10.1016/j.cej.2014. 08.037.
[22] Ebrahimi A, Ehteshami M, Dahrazma B. Isotherm and kinetic studies for the biosorption of cadmium from aqueous solution by Alhaji maurorum seed. Process Saf Environ Prot 2015;98:374–82. doi:10.1016/j.psep.2015.09.013. [23] Zhang H-B, Yang M-X, Shi W, Zheng Y, Sha T, Zhao Z-W. Bacterial diversity in mine tailings compared by cultivation and cultivation-independent methods and their resistance to lead and cadmium. Microb Ecol 2007;54:705–12. doi:10.10 07/s0 0248-0 07- 9229- y. [24] Tabaraki R, Nateghi A, Ahmady-Asbchin S. International biodeterioration & biodegradation biosorption of lead (II) ions on Sargassum ilicifolium: application of response surface methodology. Int Biodeterior Biodegradation 2014;93:145–52. doi:10.1016/j.ibiod.2014.03.022. [25] Tunali S, Çabuk A, Akar T. Removal of lead and copper ions from aqueous solutions by bacterial strain isolated from soil. Chem Eng J 2006;115:203–11. doi:10.1016/j.cej.2005.09.023. [26] Selatnia A, Boukazoula A, Kechid N, Bakhti MZ, Chergui A, Kerchich Y. Biosorption of lead (II) from aqueous solution by a bacterial dead Streptomyces rimosus biomass. Biochem Eng J 2004;19:127–35. doi:10.1016/j.bej.2003.12.007. [27] Gupta VK, Rastogi A. Sorption and desorption studies of chromium(VI) from nonviable cyanobacterium Nostoc muscorum biomass. J Hazard Mater 2008;154:347–54. doi:10.1016/j.jhazmat.2007.10.032. [28] Tamura K, Peterson D, Peterson N, Stecher G, Nei M, Kumar S. MEGA5: molecular evolutionary genetics analysis using maximum likelihood, evolutionary distance, and maximum parsimony methods. Mol Biol Evol 2011;28:2731–9. doi:10.1093/molbev/msr121. [29] Bautista-Hernández DA, Ramírez-Burgos LI, Duran-Páramo E, FernándezLinares L. Zinc and lead biosorption by Delftia tsuruhatensis: a bacterial strain resistant to metals isolated from mine tailings. J Water Resour Protect 2012;2012:207–16. [30] Murthy S, Bali G, Sarangi SK, Info P. Effect of lead on growth, protein and biosorption capacity of bacillus cereus isolated from industrial effluent. J Environ Biol 2014;35:407–11. [31] Jin Y, Yu S, Teng C, Song T, Dong L, Liang J, et al. Biosorption characteristic of Alcaligenes sp. BAPb.1 for removal of lead(II) from aqueous solution. 3 Biotech 2017;7:123. doi:10.1007/s13205- 017- 0721- x.
Please cite this article as: S. Sayyadi et al., Thermodynamic, equilibrium and kinetic studies on biosorption of Pb+2 from aqueous solution by Bacillus pumilus sp. AS1 isolated from soil at abandoned lead mine, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.09.005