Characteristics and fouling behaviors of dissolved organic matter in submerged membrane bioreactor systems

Although the significance of dissolved organic matter (DOM) in membrane bioreactor (MBR) fouling has been increasingly noted in recent studies, little information is available on the characteristics and fouling potential of DOM at the fractional level. This study sought to gain a more fundamental understanding of the complicated DOM fouling phenomenon. DOM in MBR systems was fractionated into more homogeneous components, namely, hydrophobic aquatic humic substances (AHS), hydrophilic acids (HiA), hydrophilic bases (HiB), and hydrophilic neutrals (HiN) on the basis of hydrophobicity and charge. The fractionation results revealed that hydrophobic AHS were the most abundant component of DOM in MBR systems, whereas the amount and nature of hydrophilic components were variable and sample source specific. Fouling experiments were performed in a stirred-cell filtration system with various types of DOM (i.e., original, prefiltered, and fractionated). The fouling potential of DOM was observed to be greatly affected by its characteristics, and there appeared to be a strong link between the high fouling potential of DOM and its high content of AHS. The key importance of AHS as the major foulants of DOM in MBR systems was further confirmed by the fact that AHS exhibited the highest fouling potential among the four fractional DOM components. Also, it was noted that HiN showed much higher fouling potential than HiA and HiB, and induced mainly irreversible fouling.