Experimental study of the pH, ionic strength, and reversibility behavior of bacteria–mineral adsorption

Abstract

In this study, we investigate the adsorption of Bacillus subtilis onto the surfaces of two minerals, corundum and quartz, as a function of time, pH, ionic strength, and bacteria:mineral mass ratio. Experimental results indicate that the adsorption of bacteria onto a mineral surface is a completely reversible process with equilibrium being reached in less than 1 h. Our data also indicate that B. subtilis displays a higher affinity for corundum surfaces than for quartz surfaces, and that the extent of bacteria adsorption onto corundum increases with decreasing pH, with increasing bacteria:mineral mass ratio, and with decreasing ionic strength. The adsorption behavior is governed by the chemical speciation of the bacterial and mineral surfaces. We describe the experimental results with a chemical equilibrium model. The model accounts for hydrophobic and electrostatic interactions that occur between the bacteria and mineral surfaces, and can account for the effects of solution chemistry as well as surface speciation on the extent of adsorption. These results are the first to integrate the effects of pH, ionic strength, and bacteria:mineral ratio in a quantitative model. Such an approach enables bacteria-mineral adsorption reactions to be incorporated into more standard water-rock speciation models, providing a better understanding of mass transport in both natural and bio-engineered bacteria-bearing geochemical systems.