Bacterial deposition in porous media: Effects of cell-coating, substratum hydrophobicity, and electrolyte concentration

Deposition of seven bacterial strains on spherical glass and Teflon collectors was studied in vertical downflow columns at an ionic strength (l) of 0.1 M. The various bacteria had either one of the following types of major cell-surface constituents: nonpolysaccharide (NP), amphiphilic (AMPH), or anionic polysaccharide (AP) macromolecules. Deposition was analyzed in terms of the clean bed collision efficiency alpha(0) (the probability of a cell to attach upon reaching a substratum free of cells) and a blocking factor B (the ratio of the area blocked by an attached cell to the geometric area of a cell). The value of cio decreased from 1.0 to about 0.01 in the following order of cell-surface constituents/collector combinations: NP/Teflon and AMPH/Teflon > NP/glass > AMPH/glass, AP/Teflon, and AP/glass. The value for B, at a Peclet number of 1 x 10(5), increased from about 3 to 18 in the order NP/low cell charge < NP or AMPH/high cell charge < AP/high cell charge. This indicates that cell-cell repulsion enhances blocking. Blocking is higher on Teflon than on glass. Most likely cell-surface macromolecules adsorb in the surroundings of the attached cells and enhance blocking on Teflon. The deposition of four bacterial strains was investigated at 0.0001 M less than or equal to l less than or equal to 0.1 M. For l values smaller than a critical level, alpha(0) decreased with decreasing l. The critical l is determined by the range over which cell-surface macromolecules can penetrate the repulsive Gibbs energy barrier between cell and solid. The value for B increases about 1 order of magnitude upon changing l from 0.1 to 0.001 M. Maximal control of microbial mobility in porous media can be reached in systems for which B and alpha(0) are high at high l (0.1 M): the high B value minimizes the occurrence of pore-clogging whereas the dependencies of alpha(0) and B on l allow manipulation of deposition by varying the ionic strength.