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 (/) 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 (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 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 105, 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 ≤ I ≤ 0.1 M. For I values smaller than a critical level, α0 decreased with decreasing I. The critical I 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 I from 0.1 to 0.001 M. Maximal control of microbial mobility in porous media can be reached in systems for which B and α0 are high at high I (0.1 M): the high B value minimizes the occurrence of pore-clogging whereas the dependencies of α0 and B on I allow manipulation of deposition by varying the ionic strength.