Researchers at the National University of Singapore have investigated the short-term fouling behaviour of a forward osmosis (FO) membrane in an osmotic membrane bioreactor (OMBR), using NaCl or MgCl2 as the draw solutions.

The effect of membrane orientation, mixed liquor suspended solids (MLSS) concentration, and draw solution (DS) osmotic pressure on water flux and membrane fouling behaviour was examined. The researchers also investigated the effects of simulated elevated salinity on sludge properties and membrane fouling.

Water flux and membrane fouling were not significantly affected by MLSS concentration (4.91–12.60 g/L) or osmotic pressure (3.0–15.0 MPa). However, they were severely affected by elevated salinity, due to changes in activated sludge properties – in particular increases in extracellular polymeric substances (EPS) and sludge hydrophobicity.

MgCl2 as the draw solution showed a more significant influence on activated sludge properties and membrane fouling than NaCl, but gave rise to lower salt accumulation.

Analyses of the membrane foulants showed that small sludge floc/particles and EPS (in particular, proteins) were enriched in the fouling layer.

UPLC–MS/MS analyses of the proteins showed that hydrophobic proteins were the main cause of membrane fouling.

Desalination, Volume 332, Issue 1, 2 January 2014, Pages 91–99.