Interrelated effects of aeration and mixed liquor fractions on membrane fouling for submerged membrane bioreactor processes in wastewater treatment.

The interactions of mixed liquor fractions and their impacts on membrane fouling were examined at different sparging aeration intensities for submerged hollow-fiber membrane bioreactors (MBR) in wastewater treatment. The mixed liquor samples were fractioned by size into MLSS, colloids quantified by colloidal TOC, and dissolved solutes. The experimental results showed that their significance in membrane fouling was strongly related to aeration intensity. In the absence of sparging aeration, both MLSS and colloids contributed to membrane fouling which was further enhanced by their interactions. For the tested membrane module operated at the vigorous aeration intensity typically employed in practice, however, the deposition of colloids was identified as the most important mechanism controlling membrane fouling rates. In contrast, much fewer effects were exerted by MLSS: the overall fouling rates were increased initially, and then reduced with increasing concentration of MLSS. Thus, the aeration-induced turbulence should be considered for properly assessing the mixed liquor fouling potential for wastewater MBR processes. Finally, little difference in fouling rates was observed with the use of cyclic aeration mode as compared to continuous aeration mode.