Identifications and characterizations of proteins from fouled membrane surfaces of different materials

Membrane bioreactors (MBRs) have been widely used from biotechnological fermentation to municipal and industrial wastewater treatment. However, membrane fouling is the major obstacle that hinders faster commercialisation of MBRs. Extracellular polymeric substances (EPS) secreted by bacteria are the main fouling components, which are mainly composed of proteins and carbohydrates. Although it is clear that proteins play major roles in the fouling formation mechanisms, very little is known about fouling protein characteristics. This study focused on the identification and characterization of different proteins present in EPS and their relationship with three different membrane materials, polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) in a laboratory-scale MBR setup. Results showed that the largest and the most hydrophilic (average MW = 56.14 kDa, GRAVY = −0.191) proteins deposited on hydrophilic PAN membrane, whereas the smallest and the most hydrophobic (average MW = 46.67 kDa, GRAVY = −0.001) proteins deposited on hydrophobic PTFE membranes. Smaller proteins were responsible for the fouling of membranes with large pores, and vice versa. Characteristics of chaperonin and outer membrane proteins, identified in all membranes, may facilitate the design of anti-fouling membranes.

► Proteins from the fouling layer of three different membranes (PVDF, PTFE and PAN) were characterized.
► Molecular weight and hydrophilic/hydrophobic properties of the proteins were clearly related to membrane material.
► More hydrophilic proteins with high molecular weight deposited on the more hydrophilic membrane with smaller pore size.
► Certain proteins also deposited on all membranes. These proteins may be targets for designing anti-protein fouling membrane.