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Investigation on the Ability of Pseudomonas Putida Bacterium for Biosorption of Se(IV) from the Aqueous Solutions

Esmaeili Doabsari, Fatemeh | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51695 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Outokesh, Mohammad; Keshtkar, Alireza; Sohbatzadeh, Hozhabr
  7. Abstract:
  8. In this study, biosorption of selenium by Pseudomonas putida bacteria was investigated in both single and binary uptake systems. Bacteria cells were immobilized in the chitosan beads, to study impact of microorganism entrapment on the sorption capacity of the fabricated adsorbent. Uptake capacity increased by the entrapped bacterial weight percent up to 20 wt. %; but thereafter, sorption capacity gradually leveled off with an increase in the loading percentage of the bacterial cells.The effects of the three process variables including pH (2-6), biomass dosage (0.5-2.5 g/L) and initial concentration of selenium (50-250 mg/L) on the uptake performance of adsorbent were investigated, and sorption process was optimized using response surface methodology (RSM), based on central composite design (CCD) technique. Considering the analysis of variance, achieving a low P-Value and a high F-Value demonstrated the validity of the predicted second-order model. The optimum adsorption conditions for Se(IV) at room temperature were: pH=3, biomass dosage= 1 g/L, and initial concentration = 200 mg Se /L. Under such optimum conditions, the maximum uptake capacity was predicted to be around 14.75 mg Se(IV) /(g of adsorbent) by the software Design expert V8.0.7.1. The extent of selenium uptake increased with increasing of the contact time, and equilibrium was reached within 10 h. The kinetic data were modeled using pseudo-first order, pseudo-second order, the double exponential model, Elovich model, and intraparticle diffusion equation. It was found that the uptake process can be best modeled by the pseudo-second-order rate expression (R2=0.9951), indicating that rate of the adsorption is proportional to the number of the empty sites in the sorbent material, as well as concentration of the selenium in the solution. In addition, application of double exponential model revealed the comparative effects of both internal and external mass transfer resistances.The equilibrium isotherms were determined experimentally in the concentration range of 100-400 mg/L. The data then were fitted by using two-parameter models such as Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich, and three-parameter models including Redlich-Peterson, Sips, and Radke-Prausnitz. To determine the best-fit isotherm, two selection criteria were used namely correlation coefficient, and mean square error. The error analysis demonstrated that the two-parameter models better described the selenium biosorption, compared to the three-parameter models. In particular, Dubinin-Radushkevich (D-R) equation provided the closest fitting at all examined concentrations with R2=0.967. To specify the dominant adsorption mechanism, the mean free energy parameter of the D-R model (E) was calculated. The obtained 2.952 kJ/mol value for E demonstrated that the biosorption of Se(IV) onto the biosorbent very likely occurs through a physical mechanism. In addition, the values of Langmuir selectivity factor, and the Freundlich isotherm exponent, along with the smallness of Temkin model constants, are all evidence for a strong and desirable adsorption of the selenium ion on the synthesized absorbent.The competitive biosorption of Se(IV)-Cu(II) and Se(IV)-Pb(II) onto the synthesized adsorbent was studied at different concentration of metals (50-200 mg/L), and a constant concentration of selenium (200 mg/L). According to the results, presence of Cu(II) and Pb(II) ions enhanced the selenium adsorption rate from 2.9 mg/g to 23.11 mg/L and 26.6 mg/L, respectively. This finding clearly show the synergistic effects of both Cu(II) and Pb(II) ions on the selenium adsorption. The uptake capacity of adsorbent for Cu(II) and Pb(II) in the presence of 100 mg / L selenium were obtained 10.8 mg/L and 60.685 mg/L. The greater adsorption rate of lead in this experiment, can be attributed to its higher electronegativity compared to the copper.
    The binary system data were interpreted using the multicomponent isotherms, namely: non-competitive Langmuir, and Langmuir- Freundlich models. The non-competitive Langmuir model better fitted the Se(IV) and Pb(II) binary biosorption data, because the model allows successive sequestering of two cations on a site.To determine the effect of nanoparticles on the uptake capacity of the biosorbent for selenium, different metal oxides nanoparticles were used in different weight percentages. Addition of nanoparticles did not change the extent of adsorption, appreciably. The positive effect of nanoparticles on selenium biosorption had the following order: ZnO>TiO2> SiO2. The maximum sorption capacity of Se(IV) was found to be 8.4 mg/g at 10¬ wt.% of ZnO at pH≈5, initial concentration ≈ 200 mg/l, adsorbent dosage ≈ 0.5 g/l and temperature ≈ 30℃. The nanoparticle absorption rate at 10 wt. % was also the highest :%10 > %20 > %30.Fourier transform infrared (FTIR) analysis was then utilized to characterize the ion-sequestering active sites of the biosorbent. The results revealed existence of the following functional groups that played roles in the binding process: –NH3+, –NH2, –OH-, and –COOH. Morphology of the adsorbent surface was also examined by scanning electron microscope (SEM).Finally, the biosorbent was regenerated by NaHCO3 solution. Adsorption and desorption adsorbents were repeated three times to evaluate the potential of the adsorbent for reuse. The capacity did not change remarkably after three successive cycles of sorption-desorption, which shows suitability of the synthesized material for large scale adsorption operations
  9. Keywords:
  10. Bioabsorption ; Selenium-Pyridoxine ; Chitosan ; Pseudomonas Putida Bacteria ; Modeling ; Synergistic Effect

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