Measurement of bacterial collision efficiencies in porous media

A new method, utilizing radiolabeled (³H-leucine) cells and 1-cm columns packed with 40-μm borosilicate glass beads was used to estimate bacterial collision efficiency by directly measuring the retention of cells in porous media. At a fractional retention of 0.051 (n = 3), the coefficient of variation was 0.037, permitting meaningful estimation of collision efficiencies as low as 3 × 10^-5. Collision efficiency was a function of the ionic strength and pecies identity; α increased from 1.6 × 10^-3 to 1.4 × 10^-2 for A. paradoxus in 10^-5 and 10^-3 M NaCl solutions, respectively, and from 8.9 × 10^-3 to 6.2 × 10^-2 for P. fluorescens in the same solutions. Results were not sensitive to test parameters such as velocity, volume filtered and rinse volume. The new procedure provides a convenient, reliable, accurate method for estimating low-end biocolloid collision efficiencies in porous media. In the range α < 0.01, the method is economical, significantly faster, and much more reliable than other published procedures. Its application may accelerate efforts to establish functional relationships between biocolloid collision efficiency and governing physical-chemical variables.