Biofouling control with bead-entrapped quorum quenching bacteria in membrane bioreactors: physical and biological effects.

Recently, interspecies quorum quenching by bacterial cells encapsulated in a vessel was described and shown to be efficient and economically feasible for biofouling control in membrane bioreactors (MBRs). In this study, free-moving beads entrapped with quorum quenching bacteria were applied to the inhibition of biofouling in a MBR. Cell entrapping beads (CEBs) with a porous microstructure were prepared by entrapping quorum quenching bacteria ( Rhodococcus sp. BH4) into alginate beads. In MBRs provided with CEBs, the time to reach a transmembrane pressure (TMP) of 70 kPa was 10 times longer than without CEBs. The mitigation of biofouling was attributed to both physical (friction) and biological (quorum quenching) effects of CEBs, the latter being much more important. Because of the quorum quenching effect of CEBs, microbial cells in the biofilm generated fewer extracellular polymeric substances and thus formed a loosely bound biofilm, which enabled it to slough off from the membrane surface more easily. Furthermore, collisions between the moving CEBs and membranes gave rise to frictional forces that facilitated detachment of the biofilm from the membrane surface. CEBs bring bacterial quorum quenching closer to being a practical solution to the problem of biofouling in MBRs.

Intracranial recurrence of the scalp dermatofibrosarcoma.

We report a case of recurrent scalp dermatofibrosarcoma in a 30-year-old woman who underwent surgical intervention on three separate occasions during a 60-month period, and who received post-operative radiotherapy. A small, hard, elastic mass on the right parieto-occipital scalp was initially treated by simple resection in another clinic. Despite surgical intervention and radiotherapy, a recurrent tumor associated with infiltration to the calvarium was detected. The patient was then referred to our institution and a wide resection performed. Two years later, however, the patient was readmitted to our institution as a result of tumor recurrence with intracranial involvement. Scalp dermatofibrosarcoma is an uncommon but aggressive scalp tumor; therefore, wide local excision with good margins is essential to decrease the risk of regional recurrence. Close surveillance in these cases is necessary due to late tumor recurrences.

Characterization of biofilm structure and its effect on membrane permeability in MBR for dye wastewater treatment.

Two membrane bioreactors were operated at aerobic (DO=6.0mg/L) and anoxic (DO<0.3mg/L) conditions for the treatment of synthetic dye wastewater to determine the effect of dissolved oxygen on membrane filterability. The rate of membrane fouling for the anoxic MBR was five times faster than that for the aerobic MBR. Differences in the nature of the biofilm that was formed on the membrane surface as the result of different DO level was the main factor in the different fouling rates. The biofilm structure was characterized using digital image analysis techniques. Biofilm images were obtained using confocal laser scanning microscopy (CLSM) at various operation points. Structural parameters were then computed from these images using an image analysis software (ISA-2). The structural parameters indicated that the anoxic biofilm was thinner than the aerobic biofilm but the anoxic biofilm was spread out on the membrane surface more uniformly and densely, resulting in the higher membrane fouling. Based on the extracellular polymeric substances (EPS) visualization and quantification, it was also found that EPS, key membrane foulants were spread out more uniformly in the anoxic biofilm in spite of lower amount of EPS compared to that in the aerobic biofilm.