Characterization and Significance of Sub-Visible Particles
and Colloids in a Submerged Anaerobic Membrane Bioreactor (SAnMBR)
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Abstract
The
distribution, composition and morphological structure of subvisible
particles and colloids (0.01–10 μm) in the supernatant
of a lab-scale submerged anaerobic membrane bioreactor (SAnMBR), and
their role in membrane fouling, was investigated. Photometric analysis
showed that the supernatant and membrane foulants were dominated by
particles and colloids (0.45–10 μm), which accounted
for over 90% of the total organics (proteins and polysaccharides).
Excitation–emission matrix (EEM) fluorescence spectra and monosaccharide
analysis showed that these particles and colloids were rich in fluorescent
proteins, rhamnose, ribose and arabinose, all of which could be related
to cellular and extracellular substances. Fluorescence and scanning
electron microscopy confirmed the presence of bacterial cells in/on
the subvisible particles and colloids. The microparticles (5–10
μm) were primarily composed of Streptobacilli and/or filamentous
bacteria in the form of microcolonies, while the submicrometer particles
and colloids (1–5 μm and 100 kDa-1 μm) had more
free/single cocci and bacilli. The ratio of live/dead cells varied
in different size-fractions, and the particles (1–10 μm)
contained more live cells compared with the colloids (100 kDa-1 μm).
Our findings suggest that bacterial cells in/on the particles and
colloids could have an important effect on fouling in SAnMBRs as they
represent pioneering species attaching to membranes to form fouling
layers/biofilm. Such insights reveal that previous foulant-characterization
studies in MBRs tended to overestimate organic fouling, while the
biofouling induced by these bacteria in/on the particles and colloids
was overlooked