Natural organic matter fouling due to foulant–membrane physicochemical interactions

An extended DLVO (XDLVO) force analysis was introduced to predict natural organic matter (NOM) fouling in ultrafiltration (UF) membrane processes. Ultrafiltration membrane fouling experiments were performed using two NOM extracts from real waters and two commercial polymeric UF membranes. The hydrodynamic force by permeation drag and three interfacial forces of XDLVO (van der Waals, electrostatic, acid–base energy) were used for the force analysis. Acid–base interaction forces between NOM and UF membranes were dominant in short range (separation distances < 5 nm) and appear to determine the potential of NOM deposition. Relative extents of flux decline were successfully predicted using the short-range force analyses.

Short-range force analysis using interfacial hydrodynamic and XDLVO interactions were preformed to predict for prediction of NOM fouling potential. Using this, we could suggest which component of forces effect membrane fouling dominantly. Based on force analysis, Permeation drag (PD) forces for all the cases were almost negligible compared to the other interfacial forces because of low flux (~40 mm/s) and small particle size (~1 nm). Acid–base interaction (AB) forces were dominant for a short distance (<5 nm) and determined the short-range foulant–membrane interactions. Fouling experiments for membrane and NOM supported the fouling trends predicted by force analysis. In a companion paper published in this same issue [12], we focus on biopolymer fouling of reverse osmosis membranes where the macromolecules tested are clearly colloidal in nature (see Kim & Hoek, “Interactions Controlling Biopolymer Fouling of Reverse Osmosis Membranes”). The NOM used in this study has molecular weights ranging from 1 to 10 kDa; hence, it is classically considered “dissolved,” not “colloidal.” However, according to the dynamic light scattering measurement, the organic matter exists in a size range (~1 nm) that is often considered colloidal. In a future study, the effect of solution chemistry such as existence of cation or difference of ion strength will be investigated using same approach.