Bacteriophage Adsorption during Transport through Porous Media: Chemical Perturbations and Reversibility

In a series of seven column experiments, attachment of the bacteriophage PRD-1 and MS-2 to silica beads at pH's 5.0-5.5 was at least partially reversible; however, release of attached phage was slow and breakthrough curves exhibited significant tailing. Rate coefficients for attachment and detachment were on the order of lo4 and 10-6-10-4 s-l, respectively. Corresponding time scales were hours for attachment and days for detachment. The sticking efficiency (a ) for phage attachment was near 0.01. The rate of phage release was enhanced by raising pH and introducing surface-active chemical species, illustrating the importance of chemical perturbations in promoting biocolloid transport. In a series of batch experiments, MS-2 adsorbed strongly to a hydrophobic surface, octadecyltrichlorosilane-bonded silica, a t both pH's 5 and 7. Adsorption to the unbonded silica at pH 5 was linear, but was 2.5 (with Ca2+) to 0.25% (without Ca2+) of that to the bonded surface. Neither MS-2 nor PRD-1 adsorbed to unbonded silica a t pH 7. Hydrophobic effects appear to be important for adsorption of even relatively hydrophilic biocolloids. mathematical models are available for describing transport of viruses and other colloids in soil and groundwater ( l ) , all lack data for validation. The research described in this paper is part of our ongoing studies of virus attachment and transport in natural waters. Our first objective was to determine the effect of pH on the attachment of MS-2 and PRD-1 to well-characterized silica and hydrophobic surfaces. We chose MS-2, PRD-1, and silica as their surface chemical properties are well-known, offering the potential to determine the factors controlling the degree of adsorption. We examined the importance of Ca2+ concentration and temperature in influencing MS-2 adsorption on silica a t one pH. A second objective was to demonstrate the reversibility of bacteriophage adsorption and to determine the effect of chemical perturbations on the rates of desorption. Our third objective was to test equilibrium, first-order, and two-site colloid transport models using the quantitative data and parameter estimates developed for the chemical conditions studied.