BACTERIAL DEPOSITION IN POROUS-MEDIA - EFFECTS OF CELL-COATING, SUBSTRATUM HYDROPHOBICITY, AND ELECTROLYTE CONCENTRATION

Deposition of seven bacterial strains on spherical glass and Teflon co llectors was studied in vertical downflow columns at an ionic strength (l) of 0.1 M. The various bacteria had either one of the following ty pes of major cell-surface constituents: nonpolysaccharide (NP), amphip hilic (AMPH), or anionic polysaccharide (AP) macromolecules. Depositio n 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 decr eased from 1.0 to about 0.01 in the following order of cell-surface co nstituents/collector combinations: NP/Teflon and AMPH/Teflon > NP/glas s > 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 high er on Teflon than on glass. Most likely cell-surface macromolecules ad sorb 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 va lues 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 betwee n 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 mob ility 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 occurren ce of pore-clogging whereas the dependencies of alpha(0) and B on l al low manipulation of deposition by varying the ionic strength.