Immobilization of clostridium thermocellum bacterium on coal particles for cellulosic biomass conversion

The adsorption isotherms of Clostridium thermocellum cells on bituminous coal particles of approximately 0.15-0.18 mm diameter were determined at 60°C, 45°C, and 30°C with a pH value of 7.0, and at 60°C with pH values of 6.0 and 5.0. The adsorption data were correlated with a Langmuir isotherm that was modified to account for a reduction in repulsive interaction potential at lower concentrations of adsorbed cells.

From the temperature coefficients of the equilibrium constant, the thermodynamic quantities of Gibbs free energy, ΔG, enthalpy, ΔH, and entropy, ΔS, were estimated. The enthalpy change, ΔH, was found to be in the range between -1.43 Kcal/gmol at higher cellular concentrations and -1.78 Kcal/gmol at lower concentrations which indicated that the bacterial adsorption was exothermic. The Gibbs free energy changes, ΔG, were found to be in the range between -1.74 Kcal/gmol and -0.21 Kcal/gmol indicating that adsorption was thermodynamically favorable. Free energy changes for adsorption at pH values of 6.0 and 5.0 were significantly reduced at high immobilized cell concentrations.