INJECTION-ATTACHMENT OF METHYLOSINUS-TRICHOSPORIUM OB3B IN A 2-DIMENSIONAL MINIATURE SAND-FILLED AQUIFER SIMULATOR

For some potentially useful and emerging in situ bioremediation techno logies it is important to control bacterial attachment to subsurface m aterials during the injection of microbial cell suspensions. In this s tudy the attachment patterns of Methylosinus trichosporium OB3b were m easured after horizontal injections into a two-dimensional miniature a quifer simulator containing a wet homogeneous sand. In preliminary san d column assays, bacterial attachment to the sand was increased nearly 2 orders of magnitude compared to attachment in the presence of disti lled water by raising the concentration of a pH 7.0 sodium-potassium p hosphate buffer to 10 mM. The maximal concentration of attached cells was similar to 4 x 10(8) cells/g dry sand with both sand minicolumns a nd the wet sand aquifer simulator. For the latter this occurred on str eamlines directly between the horizontal injector and withdrawal ports , where injection-withdrawal velocities were the highest. The effects of a simulated groundwater cross flow during suspension injection on b acterial attachment to the aquifer simulator sands were also studied, and a peristaltic pumping method to counteract these groundwater flow effects resulted in a more localized pattern, i.e., without extensive downstream skewing of the bacterial attachment zone. Phenol red was ut ilized as a nonbinding, red-colored tracer compound. It proved to be v ery convenient for quantitatively measuring the earlier breakthroughs of cells versus an inert tracer during the aquifer simulator and subse quent capillary tube cell injection experiments and also fdr visualizi ng the anticipated boundaries of cell attachment in the aquifer simula tor. The effect of injection velocity on the observed bacterial attach ment patterns in these experiments appears to be accounted for by coll oid filtration theory.