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

Abstract

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.

FIG. 1

Schematic diagram of the traditional experimental technique used to collect bacterial breakthrough data.

FIG. 2

Schematic diagram of the modified experimental technique used to collect bacterial breakthrough data.

FIG. 3

Effect of phosphate salt concentration on bacterial breakthrough curves; data obtained by traditional packed-bed technique. DI, deionized.

FIG. 4

Effect of 10⁻² M phosphate concentration on the absorbance of a well-stirred bacterial suspension measured using a flowthrough cell. Data for bacterial suspension in deionized water are shown in Fig. 11.

FIG. 5

Control (empty) column experiment indicating insignificant decrease in C/C_o at a phosphate concentration of 10⁻² M.

FIG. 6

Effect of phosphate salt concentration on bacterial breakthrough curves; data obtained by modified packed-bed technique. DI, deionized.

FIG. 7

Effect of 3 × 10⁻² M phosphate concentration on bacterial influent and effluent concentration and breakthrough data.

FIG. 8

Effect of 10⁻² M phosphate concentration on a representative bacterial influent and effluent concentration and breakthrough data. Average data with error bars are shown in Fig. 6.

FIG. 9

Effect of 10⁻³ M phosphate concentration on representative bacterial influent and effluent concentration and breakthrough data. Average data with error bars are shown in Fig. 6.

FIG. 10

Effect of 10⁻⁴ M phosphate concentration on bacterial influent and effluent concentration and breakthrough data. Average data with error bars are shown in Fig. 6.

FIG. 11

Representative bacterial influent and effluent concentration and breakthrough data when bacteria are suspended in deionized water. Average data with error bars are shown in Fig. 6.