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SAYAR, AHMET ALP

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SAYAR

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AHMET ALP

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2011 - 20153
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Author: DURMAZ ŞAM, SELÇEN × End date: 2020 ×

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Now showing 1 - 3 of 3
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    A sigmoidal model for biosorption of heavy metal cations from aqueous media
    (ELSEVIER SCIENCE INC, 2015) SAYAR, AHMET ALP; Ozen, Rumeysa; Sayar, Nihat Alpagu; Durmaz-Sam, Selcen; Sayar, Ahmet Alp
    A novel multi-input single output (MISO) black-box sigmoid model is developed to simulate the biosorption of heavy metal cations by the fission yeast from aqueous medium. Validation and verification of the model is done through statistical chi-squared hypothesis tests and the model is evaluated by uncertainty and sensitivity analyses. The simulated results are in agreement with the data of the studied system in which Schizosaccharomyces pombe biosorbs Ni(II) cations at various process conditions. Experimental data is obtained originally for this work using dead cells of an adapted variant of S. Pombe and represented by Freundlich isotherms. A process optimization scheme is proposed using the present model to build a novel application of a cost-merit objective function which would be useful to predict optimal operation conditions. (C) 2015 Elsevier Inc. All rights reserved.
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    Schizosaccharomyces pombe and its Ni(II)-insensitive mutant GA1 in Ni(II) uptake from aqueous solutions: a biodynamic model
    (SPRINGER, 2014) SAYAR, AHMET ALP; Sayar, Nihat Alpagu; Durmaz-Sam, Selcen; Kazan, Dilek; Sayar, Ahmet Alp
    In the present study, Ni(II) uptake from aqueous solution by living cells of the Schizosaccharomyces pombe haploid 972 with h (-) mating type and a Ni(II)-insensitive mutant GA1 derived from 972 was investigated at various initial glucose and Ni(II) concentrations. A biodynamic model was developed to predict the unsteady and steady-state phases of the uptake process. Gompertz growth and uptake process parameters were optimized to predict the maximum growth rate mu (m) and the process metric C (r), the remaining Ni(II) content in the aqueous solution. The simulated overall metal uptake values were found to be in acceptable agreement with experimental results. The model validation was done through regression statistics and uncertainty and sensitivity analyses. To gain insight into the phenomenon of Ni(II) uptake by wild-type and mutant S. pombe, probable active and passive metal transport mechanisms in yeast cells were discussed in view of the simulation results. The present work revealed the potential of mutant GA1 to remove Ni(II) cations from aqueous media. The results obtained provided new insights for understanding the combined effect of biosorption and bioaccumulation processes for metal removal and offered a possibility for the use of growing mutant S. pombe cell in bioremediation.
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    Biosorption of Ni (II) by Schizosaccharomyces pombe: kinetic and thermodynamic studies
    (SPRINGER, 2011) SAYAR, AHMET ALP; Durmaz-Sam, Selcen; Sayar, Nihat Alpagu; Topal-Sarikaya, Aysegul; Sayar, Ahmet Alp
    The potential of the dried yeast, wild-type Schizosaccharomyces pombe, to remove Ni(II) ion was investigated in batch mode under varying experimental conditions including pH, temperature, initial metal ion concentration and biosorbent dose. Optimum pH for biosorption was determined as 5.0. The highest equilibrium uptake of Ni(II) on S. pombe, q(e), was obtained at 25 degrees C as 33.8 mg g(-1). It decreased with increasing temperature within a range of 25-50 degrees C denoting an exothermic behaviour. Increasing initial Ni(II) concentration up to 400 mg L-1 also elevated equilibrium uptake. No more adsorption took place beyond 400 mg L-1. Equilibrium data fitted better to Langmuir model rather than Freundlich model. Sips, Redlich-Peterson, and Kahn isotherm equations modelled the investigated system with a performance not better than Langmuir. Kinetic model evaluations showed that Ni(II) biosorption process followed the pseudo-second order rate model while rate constants decreased with increasing temperature. Gibbs free energy changes (Delta G degrees) of the system at 25, 30, 35 and 50 degrees C were found as -1.47E + 4, -1.49E + 4, -1.51E + 4, and -1.58E + 4 J mol(-1), respectively. Enthalpy change (Delta H degrees) was determined as -2.57E + 3 J mol(-1) which also supports the observed exothermic behaviour of the biosorption process. Entropy change (Delta S degrees) had a positive value (40.75 J mol(-1) K-1) indicating an increase in randomness during biosorption process. Consequently, S. pombe was found to be a potential low-cost agent for Ni(II) in slightly acidic aqueous medium. In parallel, it has been assumed to act as a separating agent for Ni(II) recovery from its aqueous solution.