Facilitation of bacterial transport through porous media by changes in solution and surface properties

Facilitation of bacterial transport for the purpose of bioaugmentation of contaminant degradation may be achieved by a number of methods typically involving changes in the properties of the groundwater or changes in the characteristics of the bacterial surface. Facilitated bacterial transport was investigated in laboratory experiments monitoring bacterial retention in quartz sand and glass bead mini-columns. Bacterial attachment efficiencies were estimated from bacterial retention using a steady-state filtration equation. Decreased ionic strength resulted in decreased retention of A. paradoxus, with roughly order-of-magnitude decreases in retention accompanying order-of-magnitude decreases in ionic strength. Seven test chemicals were also examined in terms of their ability to modify bacterial surface properties and enhance bacterial transport. Of the seven test chemicals, the surfactants resulted in the most dramatic decreases in bacterial retention. The attachment efficiency of A. paradoxus on glass beads was lowered from 0.38 in the absence of Tween-20 to 0.0016 in the presence of 0.1 vol.% Tween-20, and from 0.064 in the absence of sodium dodecyl sulfate (SDS) to 0.0067 in the presence of 10 mg l^-1 SDS. Cell-surface modifying chemicals such as proteinase-k, EDTA, and pyrophosphate reduced bacterial attachment efficiencies. However, the reductions were less than an order of magnitude, even at the highest concentrations used. Bacterial attachment efficiencies were reduced from 0.055 in the absence of proteinase-k to 0.044 in the presence of 0.1 mg l^-1 proteinase-k, 0.61 in the absence of EDTA to 0.34 in the presence of 0.001 M EDTA, and 0.27 in the absence of pyrophosphate to 0.11 in the presence of 0.01 M pyrophosphate. Increased bacterial attachment efficiencies were observed for A. paradoxus on glass beads in the presence of 0.1 mg l^-1 lysozyme (0.74) vs. the absence of lysozyme (0.0048), and in the presence of 0.01 M periodate (0.10) vs. the absence of periodate (0.052). Changes in porous media surface characteristics were also examined. Retention of Savannah River strain A1264 on quartz sand media was observed to be less than half that on iron oxide coated quartz sand media. Coating of iron oxide-quartz by sorbed humic acids resulted in a 44% decrease in bacterial retention, a value slightly greater than that on quartz porous media. In addition to the presence of sediment organic matter, the presence of dissolved organic matter (DOM) altered bacterial retention on the porous media. DOM decreased bacterial retention on quartz (~ 20%), and increased bacterial retention on iron oxide-quartz (~ 10%).