More Efficient Media Design for Enhanced Biofouling Control in a Membrane Bioreactor: Quorum Quenching Bacteria Entrapping Hollow Cylinder.

Recently, membrane bioreactors (MBRs) with quorum quenching (QQ) bacteria entrapping beads have been reported as a new paradigm in biofouling control because, unlike conventional post-biofilm control methods, bacterial QQ can inhibit biofilm formation through its combined effects of physical scouring of the membrane and inhibition of quorum sensing (QS). In this study, using a special reporter strain (Escherichia coli JB525), the interaction between QS signal molecules and quorum quenching bacteria entrapping beads (QQ-beads) was elucidated through visualization of the QS signal molecules within a QQ-bead using a fluorescence microscope. As a result, under the conditions considered in this study, the surface area of QQ-media was likely to be a dominant parameter in enhancing QQ activity over total mass of entrapped QQ bacteria because QQ bacteria located near the core of a QQ-bead were unable to display their QQ activities. On the basis of this information, a more efficient QQ-medium, a QQ hollow cylinder (QQ-HC), was designed and prepared. In batch experiments, QQ-HCs showed greater QQ activity than QQ-beads as a result of their higher surface area and enhanced physical washing effect because of their larger impact area against the membrane surface. Furthermore, it was shown that such advantages of QQ-HCs resulted in more effective mitigation of membrane fouling than from QQ-beads in lab-scale continuous MBRs.

Preparation and application of patterned membranes for wastewater treatment.

Membrane fouling remains a critical factor limiting the widespread use of membrane processes in water and wastewater treatment. To mitigate membrane fouling, we introduced a patterned morphology on the membrane surface using a lithographic method. A modified immersion precipitation method was developed to relieve the formation of dense layer at the solvent-nonsolvent interface, that is, the opposite side of the patterned surface. Diverse patterned membranes, such as pyramid-, prism-, and embossing-patterned membranes, were prepared and compared with a flat membrane in terms of morphology, permeability, and biofouling. Patterned membrane fidelity was largely dependent on the polymer concentration in cast solution. The patterned surface augmented the water flux in proportion to the roughness factor of the patterned membrane. However, the type of pattern did not affect substantially the mean pore size on the patterned surface. Deposition of microbial cells on the patterned membrane was significantly reduced compared to that on the flat membrane in the membrane bioreactor (MBR) for wastewater treatment. This was attributed to hydraulic resistance of the apex of the patterned surface, which induced local turbulence.