Interaction energy and competitive adsorption evaluation of different NOM fractions on aged membrane surfaces

Natural organic matter (NOM) plays a key role in membrane fouling, especially in irreversible fouling. Different PVDF membrane aging degrees lead to variations in the chemical/physical properties of membrane which further affect membrane permeability and fouling behavior. In the present work, the interaction energy between foulants and membranes with different ageing degrees was assessed by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, using bovine albumin serum (BSA), sodium alginate (SA) and humic acids (HA) as model foulants. Fluorescence labeling and confocal laser scanning microscopy (CLSM) was applied to characterize the distribution rule of binary foulants formed on membrane surfaces. The calculation of CLSM images via COMSTAT could quantify each foulant distribution in the fouling layer, which provides insights on combined fouling mechanisms. Results showed that membrane ageing modifies NOM fouling behaviors in according to the degree of ageing. Furthermore, filtration of the SA/BSA mixtures showed that BSA was first absorbed on the membrane surface in a competitive environment, which then plays a bridge role in promoting the SA to form a denser cake layer on the membrane. That is to say, different ageing degrees mainly affected the attachment of BSA to the membrane surface with regard to mixture of organics.