Rapid granulation of aerobic granular sludge and maintaining its stability by combining the effects of multi-ionic matrix and bio-carrier in a continuous-flow membrane bioreactor.

The present investigation aimed at providing a novel approach to promote the rapid granulation and stability of aerobic granular sludge (AGS) in a continuous-flow membrane bioreactor (MBR). By operating two identical MBRs with or with no bio-carrier for 125 days, it was found that the combination of multi-ionic matrix and bio-carrier could promote the rapid formation and maintain the long-term stability of AGS. The primary AGS was first observed inside the reactor on day 14, and the mature AGS appeared soon and kept stable for more than 4 months (its average size still was about 800 µm on day 125). Suitable filling ratio of bio-carrier was beneficial to form a stable and regular circulating water flow inside, and adding divalent metal ions quickly reduced the negative charges of tiny sludge particles, which were two essential factors leading to the rapid granulation of AGS and maintaining its stability. The multi-ionic matrix not only enhanced the biological aggregation process, but also facilitated the expansion of the cultivated AGS into a new multi-habitat system of Mn-AGS, in which, complex microbial communities with rich bio-diversity robustly promoted the efficient removal of organic pollutants and nutrients.

Insights into the fouling layer of flat-sheet membrane and its development in an integrated oxidation ditch-membrane bioreactor.

This work revealed the characteristics of fouling layer on the flat-sheet membranes and its development in an integrated oxidation-ditch membrane bioreactor. During the operation period (130 days), the reactor performed very well in removing pollutants. As the operation proceeded, membrane fouling occurred on the flat-sheet membranes and trans-membrane pressure showed a cyclical variation. The experimental results showed that the process of membrane fouling appeared successively in two different structures: biofilm (BF) and sludge fouling (SF). The substances causing membrane fouling were mainly organic foulants and a small amount of inorganic metal compounds, especially the protein-like and fulvic acid-like substances in loosely bound extracellular polymeric substances (LB-EPS). The analysis of microbial communities revealed that SF and BF had very different microbial properties. Although most membrane foulants could be removed by physical and chemical cleaning methods, the protein-like and fulvic acid-like substances in BF were contribute much to causing irreversible membrane fouling.