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Polymeric flat-sheet membrane (FS) and ceramic flat-tubular membrane (CM) are the most widely-used membranes in anaerobic membrane bioreactor (AnMBR). However, fouling mechanism on FS and CM were rarely compared before and needed to be deeply illuminated. In this work, distinction of irremovable fouling formed on polyvinylidene fluoride FS and Al 2 O 3 CM in AnMBR treating municipal wastewater was studied. Lab-scale AnMBR operation showed that FS presented severer irremovable fouling and faster fouling rate. Foulants characterization revealed that irremovable fouling of FS was composed of more organics (FS = 0.91, CM = 0.35 g-TOC/m2-membrane) and biomass (FS = 47.3, CM = 8.65 × 1010 cell/m2-membrane), leading to gel layer loosely structured. Conversely, irremovable fouling of CM contained more inorganics (FS = 0.08, CM = 0.55 g/m2-membrane), facilitating dense gel layer with larger specific filtration resistance. Membrane cleaning tests found that gel layer on FS was efficiently removed by NaClO, while gel layer on CM was loosened by NaClO but destructed by citric acid. NaClO/NaOH both reduced resident bacteria, whereas increased the proportion of live cells. Irreversible fouling on FS involved more organics while more inorganics on CM. Irreversible biofouling could utilize citric acid as substrate for metabolism and proliferation. This study not only helps to probe fouling mechanism with different membrane materials, but also aids to develop differentiated effective cleaning strategy to corresponding membrane modules. Image 1 • Loosely structured gel layer on polymeric membrane contains more organics and biomass. • Dense and robust gel layer on ceramic membrane comprises more inorganics. • Gel layer on polymeric membrane is removed by NaClO degrading organics. • Gel layer on ceramic membrane is loosened by NaClO but destructed by citric acid. • NaClO reduces biomass on both membranes but increases the proportion of live cells. [ABSTRACT FROM AUTHOR]

Abstract: Pre-ozonation is effective in improving the membrane filterability of the mixed liquor in membrane bioreactors. However, the amelioration mechanism is still not clear. The present study systematically investigated the influence of ozonation on the properties of activated sludge, soluble microbial products (SMP), and extracellular polymeric substances (EPS). Chemical compositions of the SMP and EPS were quantified in terms of total organic carbon, polysaccharides, protein, and Ca2+/Mg2+. Functional groups were characterized using Fourier transform infrared spectroscopy and three-dimensional excitation–emission matrix fluorescence spectroscopy. On the basis of the analyses, the rationale behind the filterability improvement was elucidated. The appropriate ozonation increased the sludge hydrophobicity and introduced more acidic functional groups to the SMP and EPS, thus facilitating a sludge re-flocculation process in the subsequent aeration operation by virtue of cation-bridging and hydrophobic interactions. Ultimately, the increased sludge particle size and decreased SMP concentration jointly contributed to the amelioration of membrane filterability. [Copyright &y& Elsevier]

Despite the potentially important effect of temperature on membrane fouling, very few investigations have been conducted on full-scale membrane bioreactors (MBRs) regarding seasonal variation of fouling. In this study, fouling behavior in a full-scale MBR (capacity 60,000m3/d) in northern China was monitored for a whole year. As the mixed liquor temperature dropped from 27 to 13°C, the filtration resistance increased from 0.6×1013 to 2.6×1013 m−1, which was attributable to higher concentration of supernatant organics at lower temperatures. Humic substances were the predominant supernatant organics (10–25mg/L) in comparison with polysaccharides and proteins (both 5–15mg/L). The dependence of seasonal supernatant fouling potential on hydrophilic/hydrophobic composition and molecular weight distribution of the organics were analyzed based on statistical correlation. Humic substances in all hydrophobicity and molecular weight ranges correlated closely with the fouling potential. Hydrophilic polysaccharides and large-molecular-weight proteins were also found to contribute to the fouling potential. [ABSTRACT FROM AUTHOR]