ENHANCED TRANSPORT OF BACTERIA IN POROUS-MEDIA BY SEDIMENT-PHASE AND AQUEOUS-PHASE NATURAL ORGANIC-MATTER

Aqueous-phase dissolved natural organic matter (DOM) and sediment orga nic matter (SOM) were shown in laboratory mini-column experiments to a ffect the transport of bacteria within porous media. Attachment effici encies of bacteria were estimated from their retention on quartz, iron oxide coated quartz (Fe-quartz), and Fe-quartz coated with SOM (SOM-F e-quartz). Suwannee River Humic Acid (SRHA) and Soil Humic Acid (SHA) were used to represent organic matter (SOM and DOM), and were added to radiolabeled bacterial suspensions (10(6) cells/ml, pH = 7.7) prior t o transport. Coating quartz with iron oxide increased bacterial retent ion 160% relative to uncoated quartz. Coating Fe-quartz with SOM lower ed bacterial retention, resulting in a fraction retained only 33% grea ter than retained on uncoated quartz. Compared to these effects, the e ffect of DOM on bacterial retention was secondary, and reflected the e xtent of DOM adsorption to the porous media. When DOM did not interact with the porous media, as in the case of quartz, bacterial retention in the presence of DOM was reduced by 20%. However, when DOM adsorptio n to the porous media was increased by coating the quartz with iron ox ide, bacterial retention on the Fe-quartz increased by 10%. When Fe-qu artz surfaces were loaded with DOM to equilibrium conditions to produc e SOM-Fe-quartz, the presence of DOM in the applied solution also incr eased bacterial retention by 10%. The effects of DOM were the same for both types of humic acids (SHA or SRHA). These results suggest that S OM and DOM affect bacterial transport by increasing the negative surfa ce charge of the Pe-quartz and bacteria, respectively. The largest dec rease in bacterial retention (60%) was associated with coating of Fe-q uartz by SOM in the absence of DOM.