Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Plants, Soils, and Climate


D. W. Hendricks


R. L. Smith


The objective of this investigation was to study the effect of chemical competition on thermodynamics of bacterial adsorption. This was done using an experimental system consisting of Mendon silt loam soil as the adsorbent, Staphylococcus aureus as a common adsorbate and sodium chloride (NaCl), sodium lauryl sulfate (SLS), and peptone as competitive adsorbates.

The bacterial adsorption on soil both with and without chemical competition followed Langmuir type isotherms. From the equilibrium data, thermodynamic functions such as free energy, ΔF°, enthalpy, ΔH°, and entropy, ΔS°, were calculated. Observed positive ΔH° values indicated that the bacterial uptake in both noncompetitive and competitive environments is endothermic. Bacteria and soil both have a negative charge. A positive ΔH° value is attributed to the repulsion between the bacteria and soil particles. For a non-competitive system, the observed ΔH° value was 8.50 kcal-mole-1. Relatively higher ΔH° values were obtained in the presence of peptone and NaCl. These values were 24.0 kcal-mole-1 and 23.0 kcal-mole-1 for peptone and NaCl respectively, suggesting that the bacterial uptake is much more endothermic in the presence of these chemicals. The lower ΔH° value (3.72 kcal-mole-1) observed in the presence of SLS indicated that bacterial adsorption is relatively less endothermic in the presence of such a chemical.

In all the sorbent-sorbate systems studied, observed ΔS° values were positive indicating that the bacteria are more disordered in the adsorbed phase than they are in the solution phase. Observed ΔF° values for all the adsorption systems were negative, indicating that the bacterial adsorption in both competitive and noncompetitive environments is spontaneous.

Included in

Soil Science Commons