Transport of Microorganisms in Sand Columns

Transport of streptomycete conidia through saturated columns of uniformly packed sand was studied using miscible displacement techniques. Autoclaved sand was uniformly packed to give sand columns 20.3 and 152 cm high. Mean pore water velocities ranged from 14.4 to 131 cm/hour. A pulse of sterile water containing from 10 4 to 10 6 conidia and tagged with 36 Cl was displaced through each column with sterile water. Column effluent was collected and analyzed for conidia by serial dllution techniques utilizing starch‐casein agar. At the termination of each run, the column was sampled and analyzed for conidia distribution. For 20.3‐cm long columns, increasing the mean pore water velocity increased the maximum conidia concentration of the effluent and decreased the volume of effluent at which maximum conidia concentration was observed. Decreasing the mean pore water velocities also resulted in a broadening of the breakthrough peak and a greater volume of effluent was collected before the maximum conidia concentration was attained. Longer columns behaved as the shorter columns with the slower pore water velocities. Considerably more effluent was collected before maximum conidia concentration occurred and substantially fewer conidia were recovered from the effluent. A majority of the organisms recovered were present in the sand and a preponderance of organisms were retained near the soil surface.