Fouling mechanisms of model polymeric substances

Abstract

Extracellular polymeric substances (EPS) and soluble microbial products (SMP) have been identified as the main foulants in membrane bioreactor (MBR) operation. For a better understanding of the fouling mechanisms of these substances, filtration of model solutions with submerged membranes was carried out. Filtration was conducted following the flux-stepping method. In this work alginate was used as a model for polysaccharide, bovine serum albumin (BSA) as a model for protein, and yeast (washed and unwashed) and bentonite were used for suspended solid contents. Fouling behaviours and rejection propensities were also assessed for one-component and two-component solutions and provided explanations for fouling mechanisms of carbohydrate and its interaction with protein and membrane in MBR systems. During the filtration of most foulants (except BSA), introducing the alginate increased the reversible fouling more than the irreversible one. In addition, a different behaviour was observed for the mixture of BSA and alginate.

Submerged hollow fibre membrane filtration with transverse and longitudinal vibrations

“…Washed yeast was used as the feed in some experiments as a comparison to the unwashed yeast but without the supernatant. The washing procedures were adopted from an earlier reference of Negaresh et al [21] who removed the cell debris and soluble macromolecules (such as extracellular polymeric substances, EPS) which had been reported before as potential foulants [22]. Around 5 g of the unwashed yeast was placed in a 50 mL centrifuge tube, and then mixed with 10 times volume of milli-Q water.…”

Vibration of hollow fibre membranes in submerged membrane bio-reactors (SMBRs)

“…From Eq. (5.1), the power factor of the vibration frequency is lower than 1.5, which suggests vibration amplitude has greater impact in the transverse (Negaresh et al, 2007;Hughes and Field, 2006;Beier and Jonsson, 2009). EPS has been recognized as a main contributor to membrane fouling.…”

“…After the cleaning procedures, the permeability of the membranes was measured. If the recognized as a main contributor to membrane fouling (Negaresh et al, 2007;Hughes and Field, 2006;Beier and Jonsson, 2009). It can be adsorbed and deposited on the membrane surface thus increases the hydraulic resistance to flow (Belfort et al, 1994).…”

“…From previous references, the individual components in the reactor such as bacteria (Meng et al, 2006), yeast (Negaresh et al, 2007), proteins (Ng et al, 2006), and colloids (Rosenberger et al, 2006) can all lead to membrane fouling. The factors of ion charge and composition (Tang et al, 2007), crossflow (Zhang et al, 2011) or dead end flow, concentration (Le-Clech et al, 2003), membrane hydrophilicity (Kim et al, 2004), membrane properties (Le-Clech et al, 2003), flux (Choi et al, 2005) and hydrodynamic conditions (Jaffrin, 2008) also affect the membrane performance.…”

“…Washed yeast was used to prepare the feed suspensions in some experiments as a comparison to the unwashed yeast but without the supernatant. The washing procedures were adopted from an earlier reference of Negaresh et al (2007) who removed the cell debris and soluble macromolecules (such as EPS) which had been reported before as potential foulants (Le-Clech et al, 2006). Around 5 g of the unwashed yeast was placed in a 50 mL centrifuge tube, and then mixed with 10 times volume of milli-Q water.…”