Ünsal Açıkel

A study on the inhibition kinetics of bioaccumulation of Cu(II) and Ni(II) ions using Rhizopus delemar

The microbial growth and simultaneous bioaccumulation of Cu(II) and Ni(II) ions during the growth of Rhizopus delemar in molasses medium was investigated in a batch system. The level of Cu(II) and Ni(II) bioaccumulation and microbial growth was dependent on pH, molasses sucrose concentration and initial Cu(II) and Ni(II) ion concentrations. An increase in initial total metal ion concentration inhibited both the growth rate of fungus and the bioaccumulation capacity. Lineweaver-Burk plot of Monod equation was used to study the inhibition kinetics of bioaccumulation of Cu(II) and Ni(II) and the intrinsic and apparent model parameters were evaluated in metals-free and metals-contaminated fermentation media. The maximum specific growth rate (micro(m)) and the Monod constant (K(s)) of microorganism in metals-free media were found as 0.405 L/h and 3.977 g/L, respectively. As micro(m) remained constant in the presence of increasing concentrations of Cu(II) and Ni(II) ions, the combined inhibition of Cu(II) and Ni(II) ions on the growth rate of R. delemar was found to be a competitive inhibition. The inhibition constants for Cu(II) and Ni(II) ions were determined as 56.71 mg Cu(II)/L and 47.44 mg Ni(II)/L. As the bioaccumulation of Cu(II) and Ni(II) ions was reduced by the presence of increasing concentrations of the other metal ion, compared with the single-metal systems, the individual action of Cu(II) and Ni(II) ions on the bioaccumulation of R. delemar was generally found to be antagonistic. On the other hand, the total combined effects of Cu(II) and Ni(II) ions on the bioaccumulation of R. delemar are thought to be synergistic since the total bioaccumulated metal ion quantities per unit mass of biomass were higher than those obtained in the growth media containing Cu(II) and Ni(II) ions alone at the same concentrations.

Equilibrium, hysteresis and kinetics of cadmium desorption from sodium-feldspar using rhamnolipid biosurfactant.

In this study, the sorption/desorption equilibruim and the desorption kinetics of Cd by rhamnolipid biosurfactant from Na-feldspar as a soil component were investigated. The linear, Langmuir and Freundlich isotherms adequately fitted the equilibrium sorption data with regression coefficients ranging from 0.9836–0.9879. However, both the sorption/desorption equilibria were well characterized by the Freundlich model. The extent of hysteresis was quantified based on the differences obtained from sorption and desorption isotherms regarding the quantity of Cd(II) sorbed, the Freundlich exponent, concentration-dependent metal distribution coefficients, and the irreversibility index based on the metal distribution coefficient. The kinetics of desorption of Cd from Na-feldspar was investigated using 77 mM rhamnolipid and at pH 6.8. The first-order, an empirical first-order desorption model (two-coefficient), Lagergren-pseudo-first-order, pseudo-second-order, Elovich and modified Freundlich models were used to describe the kinetic data to estimate the rate constants. To determine the rate-controlling step, the intra-particle diffusion model was also applied to the desorption process. The desorption kinetics of Cd(II) on Na-feldspar was represented better by the pseudo-second-order, Elovich and modified Freundlich equations with correlation coefficients ranging from 0.9941–0.9982 than by first-order equations. The rate-controlling stage was suggested to be mainly the surface reaction mechanism.

Acid phosphatase production by Rhizopus delemar: a role played in the Ni(II) bioaccumulation process.

The microbial growth and activity of acid phosphatase enzyme during the growth of Rhizopus delemar in the presence or absence of Ni(II) ions were investigated. An increase in initial Ni(II) ion concentration inhibited both growth rate of R. delemar and acid phosphatase activity. The maximum-intrinsic specific growth rate (μ(m)) and Monod constant (K(s)) of microorganism in Ni(II)-free medium were found as 0.0649 h(-1) and 1.8928 g/L, respectively. The inhibition of Ni(II) ions on growth rate of R. delemar was found to be a competitive inhibition and the inhibition constant was found to be 67.11 mg Ni(II)/L. The intrinsic Michaelis-Menten constant (K(m)) and maximum forward velocity of the reaction (v(m)) were determined as 3.17 mM and 833.3 μmol/L min, respectively, in Ni(II)-free medium. In the presence of Ni(II) ions, the activity of acid phosphatase was inhibited. Addition of Ni(II) ions decreased the maximum reaction velocity, v(m), showed noncompetitive-type inhibition kinetics and the inhibition constant was determined as 50mg Ni(II)/L. Maximum Ni(II) uptake was obtained by the growing cells of R. delemar, while the uptake capacity of resting cells was lowest. This study proved that acid phosphatase enzyme participated in the Ni(II) bioaccumulation mechanism of growing R. delemar.