An improved spectrophotometric method to study the transport, attachment, and breakthrough of bacteria through porous media.

This study reports an improved spectrophotometric method for studying bacterial (Pseudomonas fluorescens UPER-1) transport and attachment in saturated porous media (silica sand). While studying the effect of ionic strength by the traditional packed-column spectrophotometric method, we encountered an artifact. The absorbance of a well-stirred bacterial suspension was found to decrease with time in the presence of high concentrations of sodium and potassium phosphate salts (> or = 10(-2) M) as the cells continued to age in a resting stage. Our results show that collision efficiency and a bed ripening index will be in error by as much as 20% if breakthrough is measured by the traditional spectrophotometric technique. We present an improved experimental technique that will minimize the artifact and should substantially advance the understanding of bacteria transport in porous media.