Effect of permeate drag force on the development of a biofouling layer in a pressure-driven membrane separation system.

The effect of permeate flux on the development of a biofouling layer on cross-flow separation membranes was studied by using a bench-scale system consisting of two replicate 100-molecular-weight-cutoff tubular ultrafiltration membrane modules, one that allowed flow of permeate and one that did not (control). The system was inoculated with Pseudomonas putida S-12 tagged with a red fluorescent protein and was operated using a laminar flow regimen under sterile conditions with a constant feed of diluted (1:75) Luria-Bertani medium. Biofilm development was studied by using field emission scanning electron microscopy and confocal scanning laser microscopy and was subsequently quantified by image analysis, as well as by determining live counts and by permeate flux monitoring. Biofilm development was highly enhanced in the presence of permeate flow, which resulted in the buildup of complex three-dimensional structures on the membrane. Bacterial transport toward the membrane by permeate drag was found to be a mechanism by which cross-flow filtration contributes to the buildup of a biofouling layer that was more dominant than transport of nutrients. Cellular viability was found to be not essential for transport and adhesion under cross-flow conditions, since the permeate drag overcame the effect of bacterial motility.