Characterization and Significance of Sub-Visible Particles and Colloids in a Submerged Anaerobic Membrane Bioreactor (SAnMBR)

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.

Influence of Ozone Treatment on Ultrafiltration Performance and Nutrient Flow in a Membrane Based Nutrient Recovery Process from Anaerobic Digestate

“…Rather young applications for ultrafiltration of biological suspensions are anaerobic membrane bioreactors [7][8][9] and the recovery of nutrients from manure and anaerobic digestates [10,11]. Anaerobic digestate is a side product of sewage sludge, animal waste, or energy crop fermentation in biogas plants.…”

Characterisation of soluble microbial products (SMPs) in anaerobic bioreactors

“…This further reinforce the idea that the carbohydrates present in wastewater measured using colorimetric assays could be wrongly estimated. The concentration is also in close agreement with other workers, who characterized PS composition in a SAMBR using simple monosaccharide analysis (Zhou et al, 2016).…”

Selective production of volatile fatty acids at different pH in an anaerobic membrane bioreactor

“…It may be assumed that, in alkaline conditions there is a general increase in protein-like compounds which can be responsible for fouling the membrane surface. On this topic, Zhou et al (2016) showed that the supernatant and foulants in an AnMBR contains more protein-like compounds compared to polysaccharides at higher operating pH. They also noted that the proteins are more likely to attach to the membrane surface when the ratio of proteins to carbohydrates is as high as 3.1 (Zhou et al, 2016).…”

“…Research studies have shown that the cake layer formation on membrane surface is aided by an intermediate layer that has a high concentration of carbohydrates. The research performed by Zhou et al (2016) involved photometric analysis showed that the supernatant and membrane foulants in a submerged anaerobic membrane bioreactor (SAnMBR) were dominated by 90% of the total proteins and polysaccharides. At alkaline condition, the rate of initial hydrolysis of organic components is higher compared to the rates in neutral to acidic pH condition (Wang et al, 2019).…”