Reversible and irreversible surface charge modification of bacteria for facilitating transport through porous media

Abstract

Reversible and irreversible surface charge modification of Bacillus subtilis (a gram-positive aerobe), Pseudomonas fluorescens (a gram-negative species) and polymeric microspheres was attempted using common chemicals. This study was undertaken to see if such chemicals could be used to alter significantly the transport of various bacterial species through porous media. Significant surface charge alterations were observed in the irreversible treatments as shown by zeta potential measurements. The changes were shown to be partly reversible as evidenced by much larger shifts in zeta potential in the presence of the chemicals. Sodium pyrophosphate was found to alter the surface charge most significantly. All three species showed similar trends. Experiments on the transport of these species through sandpacks showed that their transport was significantly enhanced by the presence of the chemicals. The excellent correlation between high surface charge and transportability clearly suggests that electrostatic interactions between bacteria and sand grains are a dominant factor in their retention. Other bacterial retention mechanisms such as polymer adhesion seem to be relatively unimportant, at least for the species studied here. The various mechanisms responsible for the improved transportability and the surface charge modification are discussed. The applications of the study to filtration and microbial-enhanced oil recovery are pointed out.