Membrane fouling characterization by confocal microscopy during filtration of BSA/dextran mixtures

The increasing use of membrane bioreactors (MBRs) mainly in wastewater treatment, have found membrane fouling as one of the major drawbacks. Membrane fouling in MBRs has been attributed to polysaccharides, proteins or nucleic acids from several origins. Therefore, membrane fouling characterization of model solutions containing a protein (BSA) and a polysaccharide (dextran) has been carried out using macroscopic data (permeate flux evolution) and microscopic analysis by confocal scanning laser microscopy (CSLM). Solutions containing fluorescent and non-fluorescent BSA and dextran (70 and 150 kDa) have been microfiltered using polycarbonate and mixed esters membranes. The results show that internal fouling is the prevailing mechanism for all the cases studied in this work, however, when the smallest dextran is present in the solution, fouling is more severe and the time needed to reach the steady state reduced. CSLM data made it possible to calculate the fraction of pore surface where protein and/or dextran were detected (Ps). Values of Ps were obtained up to a depth of 3 μm inside the membrane, and provided information about the blockage of the pores. The effect of the fluorescent probe conjugated with the protein and/or the dextran was also studied. It was observed that fluorescent solutions of BSA and dextran showed less fouling compared to the non-fluorescent solutions, this fact being more evident in the case of the mixed esters membrane.