Effects of porous media preparation on bacteria transport through laboratory columns

Bacterial and colloid transport experiments related to environmental system s are typically performed in the laboratory, with sand often used as the po rous media. In order to prepare the sand, mechanical sieving is frequently used to tighten the sand grain size distribution. However, mechanical sievi ng has been reported to provide insufficient repeatability between identica l colloidal transport experiments. This work examined the deficiencies of m echanical sieving with respect to bacterial transport through sand columns. It was found that sieving with standard brass sieves (1) contaminates the sand with copper and zinc as a linear function of sieving time and (2) inef ficiently sizes sand grains below 300 mum (the largest size examined in thi s study) due to rapid clogging of the sieves. A procedure was developed tha t allows utilization of brass sieves for sizing the sand grains and removes the metal contamination introduced from the sieves. Bacterial transport ex periments utilizing this column preparation procedure gave repeatable break through curves. Further examination of the effects of these treatments on b acterial transport showed interesting results. First, it was found that the metal contamination did not affect the clean-bed bacterial transport. Seco nd, it was found that variations of the column flushing procedure did not a lter the clean-bed breakthrough of the bacteria, but did alter the inter-pa rticle blocking. Finally, it was found that the shape of the sand grains (o blong vs. rounded) significantly alters the bacterial transport, with the t ransport being dominated by the smallest dimension of the oblong grains. (C ) 2001 Elsevier Science Ltd. All rights reserved.