Visualisation and characterisation of biopolymer clusters in a submerged membrane bioreactor

Abstract

A laboratory wastewater treatment membrane bioreactor (MBR) with a submerged hollow-fibre membrane was used to investigate the major foulants in sludge mixtures. Confocal laser scanning microscopy (CLSM) with a triple fluorescent staining protocol, i.e., SYTO9 for microbial cells, ConA-TRITC lectin for polysaccharides and NanoOrange for proteins, was utilised to visualise the fouling materials. A pool of biopolymer clusters (BPC) ranging from 2.5 to 60 μm in size was identified in the liquid phase of the MBR sludge and in the cake sludge on the membrane surface. According to the CLSM examination, BPC are free and independent organic solutes that are different from biomass flocs and extracellular polymeric substances (EPS) and much larger than soluble microbial products (SMP). Compared to EPS, BPC contain more polysaccharides and proteins and less humic substances. It is believed that BPC are an important foulant that interacts with biomass flocs to form the sludge fouling layer on the membrane. A filtration test observed with the CLSM shows that BPC are apparently formed by the adsorption and affinity clustering of SMP within the sludge deposited on the membrane surface. The cake sludge on the fouled membrane has a much higher BPC content (16.8 mg TOC/g SS) than the MBR bulk sludge (0.4 mg TOC/g SS). It is argued that BPC behave as a glue to facilitate the growth of an impermeable sludge cake on the membrane surface, thus resulting in serious MBR fouling. These CLSM findings provide the first direct evidence of the presence of BPC in MBR and illustrate their essential role in membrane fouling.

Membrane fouling in membrane bioreactors—Characterisation, contradictions, cause and cures

“…In trials with a lab-scale MBR fed on synthetic wastewater, they found a weak correlation between BPC concentration (i.e., c TOC ) and TMP as a function of productivity (permeate volume over membrane surface). The group visualised clusters ranging from 2.5 to 60 m in size [67].…”

Treatment of coal gasification wastewater by membrane bioreactor hybrid powdered activated carbon (MBR–PAC) system

“…6a and b shows that MBR-PAC in stages 1-3 suffered slightly from membrane fouling because the polysaccharide did not cause significant effect on the irreversible fouling due to a major portion of them were biodegraded (Taimur Khan et al, 2013). Furthermore, higher protein/polysaccharide ratio indicated higher hydrophobicity of sEPS (Sun et al, 2008) and the affinity between proteins and foulants should generally be greater than that of polysaccharides in relation to their hydrophobicity and surface charge (Taimur Khan et al, 2013). In day 41-50, protein/polysaccharide ratio in MBR-PAC was lower than SMBR.…”

Membrane fouling reduction and improvement of sludge characteristics by bioflocculant addition in submerged membrane bioreactor

“…The cake layer and mixed liquor were extracted and analyzed with regard to EPS and SMP based on the methods as demonstrated in our previous study [23]. BPC were obtained by following the method proposed by Sun et al [24]. In this study, the extracted samples were normalized as the sum of proteins (EPS P , SMP P , BPC P ) and polysaccharides (EPS C , SMP C , BPC C ).…”

“…More sludge cake on membrane surface could cause endogenous decay or cell lysis at the bottom layer, which led to release of more EPS P and SMP [40,41]. Furthermore, the continuous accumulation of SMP in the sludge layer generated more BPC on membrane surface, which accelerated the formation and attachment of a sticky and impermeable sludge cake on the membrane surface [7,24]. On contrary, in the MBR-G, Gemfloc Ò addition not only reduced deposition of EPS P by lowering TMP development, but also adsorbed SMP P and SMP C , resulting in less retention of BPC P and BPC C in the sludge cake.…”