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.